On the Morphology of the Cranial Muscles in Some Vertebrates. · 2006. 5. 22. · the development...

MORPHOLOGY OF CRANIAL MUSCLES IN SOME VERTEBRATES. 167

On the Morphology of the Cranial Muscles inSome Vertebrates.

ByF. II. E<1 t;ewoi-III. M.l>., D.Sc,

Professor of Medicine, University of Bristol.

With 100 Text-figures.

IN the following paper I have described .and comparedthe development of some of the cranial muscles in Scyl-lium canicula, Squalus acanthias, Acipenser sfcurio,Lepidosteus osseus, Amia calva, Salino fario, Cera-todus Forsteri, Triton cristatus, Rana temporaria,Alytes obstetricans, Bufo lentiginosus, Pelobatesfascus, Chrysemys marginata, Lacerta agilis, chick,rabbit, and pig.

The object has been to determine as far as possible themorphology of the muscles, and so to deduce a morphologicalclassification of the motor nuclei of the cranial uerves, moreespecially in mammals and man.

A subsidiary object has been to ascertain what evidence isafforded by these muscles in regard to the speculations ofzoologists on the phylogenetic relations of the various verte-brate groups.

The paper is a sequel to one previously published on some ofthe cranial muscles of Sauropsida.

The adult anatomy of the muscles has been described byVetter, Furbringer, Pollard, McMurrich, Allis, Jaquet,Driiner, Ecker and Gaupp, Mivart, Krause, and others referredto in the paper. In the majority of cases observation of thedevelopment of the muscles merely serves to support deduc-tions as to their homologies already made from consideration

VOL. 5 6 , PART 2 . NEW SERIES. 1 3

168 F. H. EDGEWORTH.

of their adult forms, but in some cases it suggests corrections.In the case of Lepidosteus only the hypobranchial muscles

have beeu described—by Fiirbinger, and the names for othermuscles have been as far as possible those used by Vetter andAllis in Ganoids and Teleostei. The cranial muscles ofPolypterus have been described by Pollard, and the hypo-branchial muscles by Piirbringer. They did not state thespecies examined. Those of P o l y p t e r u s s enega lu s (speci-mens 7$ to 9£ cm. long) differ in a few particulars fromthe descriptions given by those authors. The cranial musclesof Salmo far io have not hitherto been described, but theresearches of Vetter in other Teleostei made identificationand nomenclature possible.

Van Wijhe desci'ibed the early stages of the development ofthe cranial muscles of Scyllium ; and Miss Platt those ofNecturus; observations otherwise have been limited to thedevelopment of individual muscles or muscle-groups.

The nomenclature employed by previous writers has, ingeneral, been followed. Iu cases where different names havebeen applied to homologous muscles iu related animals achoice has been made, and this has necessitated somechanges.

The paper is divided into the following sections : (1) Thesegmentation of the head; (2) ma.ndibular muscles; (3)hyoid muscles; (4) eye muscles of the rabbit; (5) branchialmuscles ; (6) oesophageal, larynofeal, ancl pharyngeal muscles ;(7) muscles derived from trunk myotomes passing to thetipper ends of the branchial bars; (8) hypobranchial spinalmuscles; (9) lingual muscles; (10) some phylogeneticspeculations; (11) on Fiirbringer's theory of the skull; (12)a suggested morphological classification of the motor centresof the mid- and hind-brain in man.

THE SEGMENTATION OP THE HEAD.

In the body region of Scyllium embryos it is found thatthere is an unsegmented part below enclosing the ccelom, and


a segmented part above, the somite, which subsequentlyseparates from the dorsal edge of the coelotn and developsinto myotome and sclerotome.

In the head the conditions in the mandibular and hyoidsegments are different from those in the branchial segments;in the latter the lateral plates of mesoderm are at first con-tinuous ventrally with the wall of the pericardium or cephaliccoelom1 (Text-fig. 2); in the mandibular and hyoid segments

TEXT-FIG. I.2TEXT-FIG. 2.

Text-figs. 1 and 2.—Scylliivm, embryo 7 mm., transverse sections.Text-fig. 1 is the more anterior.

the lateral plates of mesoderm are continuous ventrally withthe walls of the mandibular and hyoid sections of the cephaliccoelom. These differ from the branchial sections in tliat nocommunication from side to side takes place (Text-fig. 1).In the rabbit, however (Text-fig. 76), the cephalic coelom iscontinuous from side to side in the mandibular and hyoidsegments, just as it is in the branchial segments.

1 The latter name is perhaps preferable, as pi-obably the heart origin-ally lay behind the branchial region.

- For reference letters on Text-figures see p. 314.

170 F. H. BDGEWOBTH.

The lateral plate of the hyoid segment extends upwardsand forwards lateral to the alimentary canal between the firstand second gill-clefts ; its upper end in 6^ and 7 mm. embryos( = stages H and I of Balfour) is continuous above with the" fourth myotome" of van Wijhe.

Van Wijhe says that the " fourth myotome " in stage J isseparated from the lateral plate and is very rudimentary,also that it atrophies towards the end of that period ; farther,that " bis in dieselbe Hohe aber niehr lateral verlangen sichin spateren Stadien die Wiinde der jetzigen Hyoidhohle.Mit dieser Verlangernng darf das vierte Myotome nichtverwechselt werden." The Anlage of the rectus externus,regarded by van Wijhe as the third myotome, was stated to becontinuous in stage I with the solid cell mass in the hyoidarch, and in stage J to be no longer so.

In the embryos of 6£ and 7 mm. in length ( = stages H and I)examined, it was found that the Anlage of the rectus externuswas continuous behind with the upper end of the epithelium-lined cavity in the hyoid arch, i. e. with the fourth myotomeof van Wijhe. In embryos of 9 mm. (Text-fig. 3) and 10 mm.it was found that the epithelial walls of the hyoid cavity hadcome together, so that the cavity had disappeared, that thenow solid cell column had extended upwards, and that theAnlage of the rectus externus was continuous behind withthis cell column some little distance from its upper end, at asite corresponding with the original upper end of the hyoidcavity. No trace of a separated "fourth myotome" wasseen. It is therefore possible, on the analogy of what takesplace in the trunk, to regard the whole of the " lateral plate "and " fourth myotome "—which do not become separate—astogether forming the hyoid myotome.

This theory is supported by the difficulty of finding anystructure in the body region which is homologous with thelateral plates of the head. Ziegler was of opinion that theywere homologous with the "Urwirbelkommunikation " (ofRabl), the "Ursegmentsteil" (of Felix). But it is scarcelypossible that epithelial structures of the head, which develop


into muscles, can be homologous with epithelial structures inthe body, which are the " Mutterboden fur deu verschiedenenHarnkanalchen" (Felix). Nor do the lateral plates of thehead appear to be homologous with the " Seitenplatten" (ofFelix) in thebody, for this term denotes the epitheliumlining the ccelotu.

The Aulage of the rectus externus may be regarded as a

TEXT-FIG. 3.

Scyllium, embryo 9 mm., transverse section. The line attachedto the mark * shows the point of junction of the Anlage of theexternal rectus with the liyoid niyotome.

very early anterior prolongation of the upper end of thehyoid Hiyotonie.

Ziegler was of opinion that the eye-muscles gave noevidence of the primary segmentation of the head, but attri-buted the Anlage of the rectus externus to the mandibularsegment.

The Anlage of the obliquus superior was regarded by vanWijhe as the second niyotome of the head. On the analogyof the rectus externus it may be looked upon as simply aforward projection of the upper end of the mandibular

172 P. H. EDGBWOETH.

myotome. Both these Anlagen are anterior projections fromthe upper ends of their respective myotomes, to add to themusculature of the eye, which is primarily formed from thepre-mandibular segment.

As above stated, the lateral plate of the mandibularsegment, which is serially homologous with that in tlie ljyoidsegment, may be regarded as the myotome of that segment.

In the case of the five branchial segments, the epithelium-lined cavities—the lateral plates of van Wijhe—are con-tinuous below with the cephalic coelorn. Above, they-are

TEXT-FIG. 4

Scyllhiia, embryo 14 mm., transverse section.

stated by van Wijhe to be continuous with myotonies—hissixth, seventh, eighth, and ninth. These myototnes werestated to separate from the lateral plates, and to undergovarious changes, the fifth atrophying, the sixth becomingvery rudimentary, and the seventh, eighth, and ninth forrniug"Vorn Schiidel zum Sclmltergiirtel ziehende Muskeln nebstdem vordersten Theile des sterno-hyoideus." In regard tothis asserted continuity between the myotomes and lateralplates, it is noteworthy that Ziegler says it is ''schwierig dennnten Ursprung des Ursegments mifc dem oben sichbareuMyotom in Veibindung zu bringen, und dies ist bis jeztkeinem einzigen Forscher in der richtigen Weise gelnngen."

MORPHOLOGY OP CRANIAL MUSCLES IN SOME VERTEBRATES. 173

I t might be expected that if the lateral plates are thesplanchnic elements of myotonies above, their relation to thelatter would be constant. But this is not so ; for instance,in the figure given by Ziegler of a 6"5 mm. Torpedo embryo,two lateral plates (those of the second and third branchialarches) lie beneath three myotomes—his fifth, sixth, andseventh ( = sixth, seventh, and eighth of van Wijhe), and thelateral plate oE the fourth branchial arch lies below hiseighth. In Ceratodus, according to Greil, the lateral platesof the first three branchial segments are continuous abovewith one (the first) myotome, and those of the fourth andfifth branchial segments are continuous above with onemyotome (the second). In R a n a e s c u l e n t a , with five tosix somites (Corning, '99, Taf. ix, figs. 7 and 11), the lateralplates of the first and second branchial segments lie in frontof the first myotome. To this may be added that in rabbitembryos 3 mm. long (Text-fig. 78) the first branchial lateralplate lies in front of the first trunk myotome, and the secondand third branchial lateral plates (as yet not separated) liebeneath the first trunk myotome.

Secondly, it might be expected that the lateral plate wouldin all animals be at first continuous with a rnyotonie above,but in Necturus embryos (Text-figs. 51-53) and rabbitembryos (Text-fig. 78) it is not possible to see any continuity.

Both these points have been emphasised by Agar in arecent criticism of the theory of van Wijhe. Agar's theory isthat the fourth somite of van Wijhe represents the condensedsomatic portion of the hinder palingenetic head somites, andhe points out that some observers have described more thanone somite in this situation, e . g . Brauss, two in Spinax, andMiss Platt, three in Acanthias. The difficulty in acceptingthis theory is that, as above stated, this fourth somite is, inScyllium, continuous with the lateral plate of the hyoidsegment.

Ziegler throws doubt on the existence of van Wijhe's fifthmyotome—the one which lies above the first branchial seg-ment—on the ground that in Torpedo its cavity is no more

174 P. H. BDGEWORTH.

T E X T - F I G . 5.

T E X T - P I G . 6.

Uoui tax'

Text-figs. 5 and 6.—Scyllium, embryo 16 mm., transverse sec-tions. Text-fig. 5 is more anterior. In the sections the rightside is slightly anterior to the left.

MOHPHOLOGY Oi' CRANIAL MUSCLES IN SOME VERTEBRATES. 175

than a cleft, and that it quickly becomes rudimentary. Heconcludes that it is only a small cavity in the mesenchymeand of no theoretic importance. I t is difficult to share thisopinion, for the corresponding structure in Scy Ilium is lined byepithelial cells and closely resembles the next followingmyotome (Text-figs. 1 and 2).

Ziegler counts three myotomes in Torpedo (his fifth, sixth,and seventh) corresponding to three lateral plates, regardsthe vagus as a "zusammengesetzte Nervencomplex" corre-sponding to three segments, and is of opinion that it is incorrespondence with this that the next following myotome(his eighth = van Wijhe's ninth) is the foremost to have anynerve-roots, an anterior one only. The difficulties in accept-ing such a view are : first, as stated above, the want of antero-lateral correspondence between the myotomes and lateralplates; and secondly, in Scyllium, and probably also in Tor-pedo at a later stage, a fifth branchial lateral plate is formed,i. e. there would be an overlapping of the territories of thevagus and spinal roots.

Greil's views as to the nature of the mesoderni of the headof Ceratodus are very different from the foregoing. He holdsthat the musculature of the branchial region is derived fromdowngrowths of the first two myotoines, that in the firstthree branchial arches being derived from the first myotome,that in the fourth and fifth arches from the second myotome.The cells forming these downgrowths can be distinguishedfrom the immediately subjacent lateral plates by the shape oftheir nuclei and by the later absorption of their yolk-granules.The downgrowths increase in vertical depth from behindforwards. The lateral plates of the branchial arches degene-rate into connective tissue. The dorsal portions of the firstthree arches, i. e., those which are formed from the firstmyotome, develop dorsally into the levatores arcum branchi-alum and ventrally into the second and third interbranchi-

• ales and the ceratohyoideus; that of the fourth arch into thefourth levator and fourth interbranchialis; that of the fiftharch anteriorly into the dorso-laryngeus and the fifth inter-


branchialis, and posteriorly into the fifth levator and levatorscapulas. The musculature of the hyoid and mandibularai'ches cannot be regarded as derivations either of a somiteor of a lateral plate; it never takes on lateral-platecharacteristics.

A difficulty in accepting this theory is that it does not seemto be of general applicability in Vertebrates. Thus, as statedabove, in the rabbit the lateral plate of the first branchialarch is in front of the first trunk myotome, and those of thesecond and third arches lie below the first trunk myotome;and there is a gap between the dorsal edges of the lateralplates of the second and third arches and the ventral edge ofthe first myotome. A difference in the shape of the cell-nuclei and in the rate of absorption of yolk-granules does notappear to be of sufficient importance to justify a separationinto upper and lower portions of a structure which in otheranimals has been called lateral plate. As far as I have beenable to observe, the ventral end of the lateral plate, taken inits usnal sense, does not degenerate into connective tissue,but becomes converted into muscles.

These difficulties lead to the following- theory of the seg-mentation of the head. It is probable that it originally con-sisted of five segments only—the premandibular, mandibular,hyoid, first branchial, second branchial—each having- a myo-tome, which, in the case of the four latter, contains a slit-like,epithelium-lined cavity continuous with the cephalic coeloinbelow. To each myotome passed a nerve—the I l l rd, Vth,Vllth, IXth, and Xth.1 The gill-clefts are intersegmental.New segments were added, one by one, behind the secondbranchial, the head extended back into the body-region, and

1 According to Neal ('98) only one encephalomere corresponds to thevagus—a fact which, if the encephalomeres have segniental, or ratherinter-segmental, worth, agrees with the theory that the vagus is not a" zusammengesetzte Nervencomplex," but primarily, as regards itsmotor branches, of one segment only—the second branchial—and thatadditional branches were developed as the number of gill-clefts andbranchial segments was added to.

MOHPHOLOGY OF CRANIAL MUSCLES IN SOME VERTEBRATES. 177

the added myotomes necessarily lie beneath the anterior bodymyotonies, with their upper ends at varying distances from theventral surface of the latter, with which they may or maynot agree in antero-posterior extent. In R a n a e s c u l e n t a ,with five to six somites, the most anterior trunk myotomelies above the third branchial, i . e . the first added myotome;a little later there is a relative shitting forward of the trunkmyotomes, so that the first trunk myotome comes to lie abovethe first branchial myotome (see Coming's figures, Taf. ix,figs. 7, 11, and 26). In Scyllium this overlapping is, second-arily, antedated in development, so that the first branchialmyotome never lies in front of the first trunk myotome. Inthe rabbit it does so.

The backward growth of the head into the body by thisprocess of metameric increase leads to the non-developmentof the ccelornic portion of the anterior trunk-somites. InScyllium, for instance, the first four trunk-somites have nocoolomic portions.

In the head, as in the body, each myotome is at first anepithelium-lined cavity, which is continuous below with thecoelom. The differences between the myotomes of the bodyand those of the head are : (1) Whereas in the body theinyotomes extend dorsally to the mid-dorsal line, and, subse-quently, ventrally outside the somatopleure wall of the coelomto the mid-ventral line, neither of these secondary phenomenatakes place in the head ; (2) whereas the coelom is large inthe body and contains the alimentary canal and otlier viscera,it is small in the head and lies entirely ventral to the alimen-tary canal; (3) in correlation with this the myotomes of thebody lie, at first, dorso-lateral to the alimentary canal, thoseof the head lie dorso-lateral and lateral to i t ; (4) the sclero-tome elements of the body-myotomes are formed by ventro-medial outgrowths, those of the head from scattered cellsgiven off from the premandibular, mandibular, and hyoidmyotomes. These differences are intimately associated withthe development of gill-clefts and a crauiuin in the head, ofviscera and a vertebral column in the body.

178 F. H. JKDGBWOETH.

If, following Fiirbringer, it be supposed that primitivelythe myotomes lay exclusively lateral to the chorda dorsalis, itwould follow that they have taken different paths of develop-ment in the head and body, resulting in the conditions abovestated.

According to the generally accepted theory, certainSelacliii, e . g . Heptauchus, are the most primitive of gnatho-stome Vertebrates, in that they have the greatest number ofbranchial segments; and the lessened number of branchialsegments in Teleostomi, Amphibia, and Dipnoi is due to adisappearance of the hinder ones. If, however, it be supposedthat the original number of branchial segments was two, i . e .first and second, and that these were added to by a process ofmetameric increase, the interesting question arises as to theleast number present iu these Vertebrate groups, for this maybe supposed to have been possessed by some primitive form.The Amphibia have four branchial segments, Dipnoi and mostTeleostomi five (though Polypterus has only four), and mostElasmobranchs five, though they may have as many as seven.I t may therefore be supposed that the original numberpresent iu Amphibia was added to in the other groups. Thisharmonises with the conclusion, stated later, that the conditionof the muscles of the head in Amphibia is more primitive thanin Dipnoi, Teleostomi, and Elasmobranchs.

The lessened number present in Sauropsida and Mammaliamay be supposed to have resulted from reduction of the hinderof these four branchial segments. In the later stages ofReptiles, previously investigated,only two branchial myotomeswere seen, but the early stages of C h r y s e m y s m a r g i n a t ashow four. In Gallus ouly two are present, even in the earlystages. In Lepus only the first three are developed.

The cephalic coelom disappears in the mandibular andhyoid segments early in development, and its walls developinto the intermandibularis and interhyoideus, which are atfirst continuous with the mandibular and hyoid myotomes.The lower ends of the branchial myotomes separate from thewall of the branchial portion of the cephalic coelom, and they

MORPHOLOGY OF CRANIAL MOSOLES IN SOME VERTEBRATES. 179

develop into the branchial muscles. No muscles are directlyformed from the walls of the branchial portion of the cephalicccelom, which subsequently retreats from the liead.

MANDIBULAK MUSCLES.

Scyl l ium.—On the formation of the palato-quadrate, in16 mm. embryos, the inandibular niyotome lies outside of andacross the palatine process, and then separates into an upper

TEXT-FIG. 7.

Scyllium.. embryo IV mm., transverse section. The right side ofthe section is slightly anterior to the left.

levator maxillao superioris and lower adductor mandibulae,the process beginning in 20 mm. embryos (Text-fig. 11). Theseparation of these two muscles by the palato-quadrate is com-plete, and this is also the case in Acanthias, where, acccord-ing to Marion, the hinder portion of the levator maxillae superi-oris—forming a separate first dorsal constrictor—is insertedinto the lower jaw. This must consequently be the result ofsecondary downgrowth. The upper edge of the adductormandibulas gains, anteriorly, an additional origin from thesuborbital cartilage in 30 mm. embryos (Text-fig. 17), andthis anterior portion of the adductor separates, in 40 mm.

180 F. H. E.DGEWORTH.

embryos, forming the levator labii superioris (or add. j3) ofVetter. l a 45 mm. embryos the add. 7 of Vetter is begin-ning to be delatninated from the outer face of the adductor,and the hindmost fibres of the adductor have grown downinto the intermandibularis, forming a band similar to thatdescribed in Acanthias by Vetter.

The intermandibularis (Cs3 of Vetter, C3mv of Ruge) isformed from the ventral parb of the mandibular cavity,

TEXT-FIG. 8.

/ ^ " " ^ c o v . ^

Scyllivim, embryo 17 mm., transverse section.

which, as mentioned above, does not meet its fellow in themid-ventral line, but passes backwards ventro-median to theventral end of the hyoid cavity to open into the front end ofthe cephalic cceiom. It results from this that there is nodevelopmental stage in which the intermandibularis liesaltogether in front of the interhyoideus. It gradually exteudsbackwards, underlying the interhyoideus, so that in 23 mm.embryos its hinder edge lies posterior to the ventral ends ofthe ceratohyals (Text-tig. 12).

The nictating muscles of Scyllium (Ridewood) consist of alevator palpebras nictitantis, retractor palpebras superioris.


and constrictor spiracnli—all innervated by the Vth. liide-wood supposed that the first-named was differentiated from thesame tract as the levator maxillae superioris and that thesecond belonged to the same category, whilst the constrictorspiraculi appeared to belong to a purely dermal system ofmuscles.

According to Harman, the musculature of the eyelids ofMustelus arises "from two original sources—one a superficialdermal layer, the other a portion of a deeper dermal musclelayer/ ' the former originating from " a mass which appears

TEXT-FIG. 9.

Scylliuni, embryo 20 mm., longitudinal horizontal section throughfirst branchial segment on left side.

first in the region of the branchial bar which is the secondafter the spiracle," the latter from a mass which separatesinto " a maxillary mass and a spiracular mass/ ' Harmanalso stated that " t he progressive growth of the spiraclemuscles in the service of the face can be traced to their fulldevelopment in the facial muscles of man."

In Scyllium the Anlage of the nictating muscles can be seenin 30 mm. embryos (Text-figs. 16, 17) as a mass of cells beingproliferated from the outer surface of the upper end of thelevator lnaxillaa superioris. In 40 mm. embryos the masshas become partially divided into a deeper and a moresuperficial layer—the former is the Anlage of the levator


TEXT-FIG. 10.

Text-figs. 10 and 11.—Scyllium, embryo 20 mm. Text-fig. 10is the more dorsal.


palpebrse nictitantis, the latter that of the retractor palpebraesuperioris. In 45 ram. embryos, the latter sends downbehind the spiracle an offshoot which develops into the cou-strictor spiraculi. All these muscles in Scyllium are thusdeveloped from an Anlage budded off from the levatormaxillaa superioris. I t may be added that the facial musclesof mammals a.re hyoid in origin, formed from the upgrowinginterhyoideus (pp. 221 and 222), and consequently are nothomologous with the eyelid muscles of Scyllium.

The myotome of the mandibular segment in Teleostornanembryos lies at first across and outside the palatine process ofthe quadrate (Text-fig. 23) and then divides into parts a.boveand below this. The division takes place in Acipenser in7-g- mm., in Lepidosteus in 8-j- mm., in. Anna in 6-j mm., andin Sal mo in 5 mm. embryos. The part above the palatineprocess is the levator maxillae superioris, the part below theadductor mandibulas. From the upper end of the levatormaxillaa superioris of Lepidosteus, Amia (Text-fig. 28), andSal mo, is given off the dilatator operculi, which extends back-wards below the first gill-cleft into the opercular fold, and theremainder forms the levator arcus palatini, which is insertedinto the pa.lato-quadrate (Text-fig. 28). In Acipenser thelevator niaxillaa superioris does not divide into levator arcuspalatini and dilatator operculi; it grows backwards, withouthaving had any temporary insertion into the palato-quadrate,and becomes inserted into the hyomandibula,, forming theprotractor hyomandibularis (Text-figs. 18, 19, 20).

The dilatator operculi is partially inserted into the hyo-mandibula in Lepidosteus, and wholly in Polypterus, ? species,described by Pollard/but in P o l y p t e r u s s e u e g a l u s it passesbackwards in the outer wall of the spiracle and is insertedinto skin only (Text-figs. 35, 36). The adductor mandibulee, atfirst passing from the palato-quadrate to Meckel's cartilage,

1 Protractor ljyoniandibularis of Pollard, but not homologous withthe protractor liyomandibularis of Acipenser, as be describes a levatormaxillae superioris (i.e. levator arcus palatini), and this is also presentin Polypterus senegalus.

VOL. 56, PART 2. NEW SEMES. 14

184 F. H. E0GBWOETH.

ia. 12.

out

13.Text-figs. 12 and 13.—Scyllium, embryo 23 mm. Text-fig. 12

is the more anterior.

MOEPHOLOGY OF CRANIAL MUSCLES IN SOME VERTEBRATES. 1 8 5

undergoes various changes in the specimens examined. InAcipenser embryos up to the length of 11 mm. it remainsundivided, but in the adult (Vetter) it has additionally spreadup to the skull. In Salmo it additionally spreads backwardsto thehyomandibula. In Lepidosteus, Amia (Text-figs. 28, 34),and probably (vide infra) Polypterus, the adductor inandi-bulte divides into internal and external portions. In Lepi-dosteus (Text-figs. 26, 27) the internal portion extends upwardsoutside the palato-quadrate to gain an additional origin fromthe cranial wall; whilst the external portion, keeping itsoriginal origin, arises from the external surface and upperend of the quadrate outside the insertion of the levator arcuspalatini. In Amia1 the internal portion (in 11 mm. embryos)sends forwards a projection from its upper end which formsthe muscle connected with the olfactory chamber (LAP6 ofMcMurrich, LMS4 of Allis); in 14 mm. embryos the re-mainder of the internal portion extends upwards above thelevel of the palato-quadrate and divides into three parts(LAP2, 3) 4 of McMurrich, LMS3, i, s of Allis). The externalportion of the adductor additionally extends backwards tothe hyomandibula in 9 mm. embryos, and divides into theparts described, as parts of the adductor, by Allis.

In Polypterus, Pollard described the adductor as consistingof three parts, the pterygoid, temporal, and masseter3; of

1 The adult condition of tile mandibular muscles of Amia has beendescribed by McMurricli and by Allis. McMurrich stated that theyconsist of a levatoi1 arcns palatini and an adductor niandibuliB, andthat the former is divided into five parts—from behind forwardsLAP,, ., 3, 4, ; ; of these LAP, is inserted into the metapterygoid withsome of its hindmost fibres into the opercnlum, LAP2, 3, 4 join theadductor, and LAP5 is in connection with the olfactory chamber.Allis separated LAPj into a dilatator operculi and a levator arcuspala.tini, whilst LAP.,, 3, 4, 5 he called the second, first, third and fourthdivisions of the levator maxilla; superioris. He suggested that LAP4 and5

(LMS:i and 4) are derived from add. j3 of Selachians, and that (his)levator arcus palatini and dilatator operculi are the homologue of add.y of Selachians. From the embryological findings mentioned above itwould appear that a new nomenclature for LAP;, 3, 4, 5 (= LMS;, j , 3, 4)is needed—in terms of an internal adductor.

3 Pollard thought that the pterygoid and temporal were the homologue


these the pterygoid aud temporal are together the homologueof the internal adductor, and the masseter the homologue ofthe external adductor, of Lepidosteus and Amia.

TEXT-FIG. 14.

TEXT-FIG. 15.

ik.K-

15.Text-figs. 14 and 15.—Scyllrani, embryo 28 mm., longitudinal

horizontal sections. Text-fig. 14 is the more dorsal, throughsecond, third, and fourth branchial segments on left side.

of Add. /3 of Selachians, but this is not possible. In Text-fi gs. 35 and 361have denoted his " masseter " by the term " external adductor," and hispterygoid and temporal might be called parts of the internal adductor.

MORPHOLOGY OF OEANIAL MUSCLES IN SOME VEETEBEATES. 187

The intermandibularis of Teleostoman embryos forms, atfirst, with its fellow, a transverse muscle attached laterally toMeckel's cartilage (Text-figs. 23, 24, 28).

In Salmo it does not extend backwards, but does so inAcipenser, Lepidosteus, Amia and Polypterus, and partiallytinderlies the fore part of the interhyoideus. In Salmo,Polypterus,1 and Lepidosteus, it remains single, in Acipenserand Amia it divides into anterior and posterior parts. In

TEXT-FIG. 16.

Scyllium, embryo 30 mm., transverse section.

Acipenser the intermandibularis anterior (Cs6 of Vetter) isattached laterally to Meckel's cartilage, and the intermandi-bularis posterior (Csj and Cs3 of Vetter) spreads upwards,laterally, towards the skull.8 In Amia both intermandi-bularis anterior3 and posterior4 are attached laterally to

1 Intermaxillaris anterior of Pollard.2 All these parts ai-e innervated by the Vth (Allis).3 Intermandibvilaris of Allis.4 Superficial or inferior portion of geniohyoid of Allis ; the muscle has,

however, no genetic relation to the superior portion of the geniohyoid(called in this paper " hyoinaxillaris ") which is developed in the hyoidsegment.


Meckel's cartilage (the process of separation into anterior andposterior portion beginning in 9-i mm. embryos and beingcompleted in 14 mm. embryos).

In Ceratodus tlie myotome of the mandibular segmentspreads upwards lateral to the Grasserion ganglion (Text-fig.39), and separates from the lateral half of the intermandibularisbetween stages 40 and 42 (of Semon). It divides into outerand inner portions—ptevygoid1 and temporal3—the former ofwhich, in stage 48 (Text-fig. 46), arises from the trabecularwall, and the latter from the anterior and outer surface of thequadrate. The intermandibularis3 joins its fellow in a medianraphe and becomes attached laterally to Meckel's cartilage ;its posterior edge extending backwards underlies the forepart of the interhyoideus (Text-figs. 41, 45).

In Necturus (Miss Platt) the mesothelium of the mandi-bular arch (here interpreted as "myotome") divides into aninternal part, the temporal (here called,following Druner, the"pterygoid"), and an external part, the masseter. In Tritonthe myotome of the mandibular segment also divides into aninternal and an external part; the upper end of the internal,pterygoid, part extends up to the side of the skull; theexternal part, at first arising from the suspensorium only,divides into an outer portion, the masseter, which keeps thisorigin, and an inner portion, the temporal, which extends upto the auditory capsule.

The intermandibularis of Necturus4 remains single, itsposterior edge underlies the anterior interhyoideus (Text-fig.55); in Triton the intei'mandibularis (in larvse between thelengths of 8-|- and 10 mm.) divides into anterior and posteriorparts,6 the latter of which partially underlies the inter-hyoideus.

1 Pterygoid of Jaqtiet.• Adductor mandilmke seu digastricus of Jaquet.3 C2mv of B/uge ; znylohyoideus para anterior of Jaquet.* Myloliyoideus anterior of Mivart and Miss Platt.5 Interniaxillaris anterior and posterior of Wiedersheim; inter-

niandibnlaris anterior and posterior of Driiner.


The myotome of the mandibular segment of Rana separatesfrom the lateral half of the intermandibularis in 5 mm.embryos; it extends backwards in 7 mm. embryos, dividinginto internal and external portions (Text-fig. 58). The myo-tome thus comes to lie in a nearly horizontal position internalto the muscles developed in the hyoid segment. The internalportion develops into the pterygoid muscle, the external intothe temporal, sub-temporal, extra-temporal, and masseter

TEXT-FIG. 17.

luc.Cat.rtt.Aiv

ScyIlium, embryo 30 mm., longitudinal vertical section.

(Text-figs. 59, 60). The masseter and extra-temporal arisefrom the internal surface of the processus muscularis of thepalatoquadrate bar. The anterior end of the pterygoid shiftsoutwards beneath the anterior ends of the other muscles and isinserted into the outer end of Meckel's cartilage. The tem-poral is iuserted into the inner end of Meckel's cartilage; themasseter is inserted into Meckel's cartilage a little distancefrom its outer end ; the subteinporal is inserted, by twotendons, into Meckel's cartilage and the superior labial car-t i lage; the extra-temporal divides into two portions, one of

TEXT-FIG. 18.

Text-figs. 18 and 39.—Acipensev, embryo 8 mm. Text-fig. 18is the more anterior.

MORPHOLOGY 01' CRANIAL MUSCLES IN SOME VERTEBRATES. 191

which joins the temporal (Text-fig. 60) and the other the sub-temporal.

The muscles of Alytes, Bufo l e n t i g i n o s u s , and Pelo-bates1 are similar to those of liana (Text-fig. 63), except thatthe extrii-temporal is iuserted only into the superior labialcartilage.

The Anlage of the levator bulbi is given off from the uppersurface of the hinder part of the temporal in 9 mm. larva;;its outer end becomes inserted into the skin and upper edgeof the palato-quadrate bar ; it remains relatively undevelopeduntil late in metamorphosis. On the development of the lowereyelid a slip is separated frotn the levator bulbi, forming thedepressor palpebrte inferiors.

At metamorphosis, on the atrophy of the superior labialcartilage the sub-temporal and extra-temporal fuse with thetemporal, and the muscles become more vertical in positionon the rotation of the palato-quadrate bar.

The Anlage of the intevmandibularis of Rana divides in7 mm. embryos into three parts—the submentalis, the man-dibulo-labialis, and the submaxillaris. The submentalisdevelops later than the other two muscles ; in 12 mm. embryosit forms a mass of small round cells lying beneath andextending backwards from the inferior labial cartilages, andat the beginning of metamorphosis forms a layer of trans-versely directed muscle-fibres connecting together the infe-rior surfaces of the inferior labial cartilages (Text-fig. 60).The mandibulo-labialis, arising from the inner aspect of thetransversely directed Meckel's cartilage, passes down externalto tlie genio-hyoid and is partially inserted into skin, partiallyinterlaces with the muscle of the opposite side (Text-fig. 60).

The snbmaxillaris arises from the under surface of Meckel'scartilnge. The conditions in larvte of Bufo l e n t i g i n o s u s

1 This account differs from that of Sclrultze, in that the subtemporalis stated to be inserted into Meckel's cartilage as well as into thesuperior labial cartilage, and in the description of an extra-temporal.The results were obtained from serial sections of larvue, 10, 13, 22, and30 mm. long.

192 F. H. EDGEWOBTH.

TEXT-FIG. 20.

Text-figs. 20 and 21.—Acipenser, embryo 8^ mm. Text-fig. 20is the move anterior. The right side of the sections is slightly-anterior to the left.

MORPHOLOGY OF CRANIAL SlUSOLES IN SOME VERTEBRATES. 193

are similar to those of Rana; in Alytes the submaxillaris ai-ises,like the mandibulo-labialis, from the inner aspect of Meckel'scartilage, so that the two muscles are much more continuousthan is the case in Rana, Bufo, and Pelobates. The con-dition in 10 mm. larvte of Pelobates is similar to that of12 mm. larvss of Raua; in 13 mm. larvse the mandibulo-labialis has spread additionally into the upper lip, the couditiondescribed by Schultze. He states that the snbmentalis isattached to the inner aspect of Meckel's cartilage, but up tothe stage of 3U mm. it is attached, as in Rana, Bufo, and Alytes,to the inferior labial cartilages, as a very minute transversemuscle.

At metamorphosis in Rana, the attachment to the skin oEthe mandibulo-labialis is lost, and the muscle forms one sheetwith the submaxillaris.1

Observations on the development of the mandibularmuscles have been made by Renter in pig-embryos, andin regard to the tensor tympani by Futamnra in humanembryos. Reuter stated that the mandibular muscles arefirst visible in pig embryos measuring 16 mm. in " Nacken-Steisslange"2 in the form of an inverted Y, the two limbs ofwhich lie on either side of the lower jaw. The temporaldevelops from the upper limb, the masseter from the lowerexternal limb, and the two pterygoids from the lower internallimb. No mention is made of the tensor tympani or thepalatine muscles. According to Futamura the tensor tympaniand tensor veli palatini form a " ganz einheitlichen Muskel"in human embryos of seven weeks. This Anlage and thelevator veli palatiui are developed about the branches of thepalatine nerves from a " MuskelblastemgewebeJ) which" deutlichen Zusammenhang mit dem tiefen Teil der Platys-maaulage erkennen liisst." " Die Nervenaste fin- diese

1 Submaxillaris of Ecker and Gaup.- This stage is an advanced one, as the figures show that the ossification

of the lower jaw has begun. The Anlage of the mandibular muscles"was quite evident in a pig embryo of S mm. crown-rump measurement,from which Test-fig. 98 was taken.

194 ]?. H. BDGEWOETH.

Muskeln lassen sich leicht vom Facialis hervorfolgen."1

He also states that in pig embryos the levator veli palatiniand M. uvults develop as in man from "Grewebe desPlatysma colli das von der vorderen Seite des Oberkiefer-fortsatzes nach seiner medialen Seite zieht."

In 2 mm. embryos of the rabbit the cells which will formthe myotorne of the mandibular segment cannot be differen-tiated from the other cells occupying the segment. In3 mm. embryos (Text-fig. 76) the myotome is visible, and thewalls of the mandibular section of the cephalic ccelom arebeginning to come together, forming the intermandibularis.The myotome separates from the lateral edge of the inter-mandibularis in 7 mm. embryos. In 13 mm. embryos it haspartially separated into external and internal portions, whichform the two limbs of a A-shaped mass, the apex of whichlies just below the Gasserian ganglion (Text-figs. 94, 95); theexternal portion is the Anlage of the temporal masseter andexternal pterygoid muscles; it extends up to the skull in16 mm. embryos, the external pterygoid is cut off from theinternal surface of the lower end of the temporal. Theinternal portion separates into internal pterygoid and tensortympani. The intermandibularis forms the mylohyoid of theadult; it is covered over, in 10 mm. embryos, by the forwardgrowing interhyoideus.

The Homologies of the M a n d i b u l a r Muscles.—Com-parison of the various ways in which the xayotome of the mandi-bular segment develops shows that they may be reduced to twotypes : (1) That in which the myotome does not divide intoupper and lower portions—Ceratodus, Necturus, Triton, Rana,Alytes, Bufo l e n t i g i n o s u s , Pelobates, Lepus. (2) That inwhich the myotome divides into portions above and belowthe palato-quadrate, into levator maxillge superioris andadductor inandibulse—ScyIlium, Aeipenser,Lepidosteus, Amia,Salmo, Sauropsida.

Driiuer supposed that a portion homologous with the1 Beevor and Horsley showed, however, that no movement of the palate

is produced in the monkey on intra-cranial stimulation of the Vllth.

MORPHOLOGY OF CKANIAL MUSCLES IN SOME VEKTJSBKATES. 195

levator maxillas superioris of Selachians disappears inAmphibia.1 There is, however, no trace of this in the on-togeny of Amphibia. According to Gaupp the pterygoidprocess of Amphibia presents features which lead to the

TEXT-FIG. 22.

bvtrax

oil. vuvtm

2 2 .

Acipenser, embryo Si mm. Tlie left side of the section isslightly anterior to the right.

suggestion that it is in process of "Riickbildung." If thisbe so, and if the pterygoid process of Amphibia be homo-logous with that of Selacliians—a matter which Gaupp says

1 The levatov niaxillas supevioris "ist wohl mit der Vevwandlwng derStreptostylie in die Moniinostylie der Urodela verloren gegmigeu."

196 F. H. JGDGEWORTH.

is not certain—it might be supposed that a muscle stripwhich formerly divided into upper and lower portions now bysome atavistic process no longer does so. On the other hand,the fact that, in all the animals of: the second class, the myo-tome, undivided, lies at first across and unattached to thepalato-quadrate, i . e . shows a condition which is the perma-nent one in Amphibia and Ceratodus, suggests that the con-

TEXT-MG. 22A.

22 . a..Acipenser, embryo 9 mm.

dition in Amphibia, Ceratodus, and Mammalia is the primaryone, and that the one present in Selachii, Teleostomi, andSauropsida is a secondary one. I t would follow that thepalatine or pterygoid process of the quadrate was not primarilya process for attachment of muscles nor an upper jaw.

Fiirbringer divided Vertebrates into two classes withregard to the connection of the quadrate with the skull—those with movable quadrates (streptostylic), and those withimmovable quadrates (monimostylic). The latter condition,

MOIiPHOLOGY OP CRANIAL MUSCLES IN SOME VERTEBRATES. 1 9 7

he thought, was secondary to the first. "Die Monimostylieallgemein von der Streptostylie ableitet."

The development of the mandibular muscles in the Sau-ropsida suggests that in them there are two streptostylic con-ditions—a primary streptostylic pterygo-quadrate in birds,and a secondary streptostylic quadrate in L a c e r t a ve ra ,

TEXT-FIG. 23.

23.Lepidosteus, embryo 8 mm., transverse section.

Rbiptoglossa, and Ophidia, and that the monimostylie con-dition of Chelonia, Giocodilia, and Rhyncocephalia wasdeveloped—and probably independently—from a primitivestreptostylic pterygo-quadrate which has been preserved inBirds (loc. cit .) .

The development of the mandibular muscles in Amphibiaand Ceratodus affords no evidence that the monimostylie con-dition there present has been derived from a streptostylicone, and a fixed quadrate would appear to be a necessary

198 F. H. EDGEWOJJTH.

correlative of an undivided tnandibulav myotome, to form apoin t d ' appu i for the lower jaw.

It would follow that the streptostylic condition present inSelachians, Teleostomi, and Sauropsidan embryos is onewhich developed in correlation with a division oE th-e myotomeinto upper and lower parts, inserted into and arising fromthe palatine process of the quadrate.

TEST-FIG. 24.

2 4 .Lepidosteus, embryo 12 mm., transverse section.

In Ceratodus, Amphibia, and Lepus, where the mandi-bular myotome does not become divided into upper and lowerparts, it separates into internal and external portions. In theAnuran larvae the outer division divides into parts, some ofwhich have a temporary insertion into the superior labialcartilage, and the whole myotome assumes a nearly hori-zontal position in correlation with that of the palato-quadratebar; at metamorphosis both bar and muscles rotate into amore vertical position. In the rabbit the inner division sepa-rates into the internal pterygoid and the tensor tympani

MORPHOLOGY OF ORANCAL MUSCLES INT SOME VERTEBRATES. 199

muscles, the outer division into t h e temporal; rnasseter, a n dexternal pterygoid.

Secondaiy changes take place in the levator maxillassuperioris and adductor mandibulaD in all the animals inves-t iga ted ; no one preserves them as such. I n ScyIlium the

TEXT-FIG. 25.

2 5 .

Lspidosteus, embryo 14 mm., transverse section.

Anlage of the nic ta t ing muscles is proliferated from thelevator maxillse superioris, and add. (3 and add. \ are sepa-ra ted from the adductor. I n Teleostomi the levator maxillsesuperioris either forms a protractor hyomandibularis ordivides into a dilatator operaculi and levator arcus pa la t in i ;and the adductor may either remain single as in Salmo, ordivide into external and internal portions, of which ei ther theinternal (Lepidosteus), or botli (Amia, Polypterus) , or ? the

VOL. 56, PART 2. NEW SERIES. 15

TEXT-FIG. 26.

0« . IOtl.iivf.

2 7 .

Text-figs. 26 and 27.—Lepidosteus, embryo 19 mm. Text-fig. 2is the more anterior.

MORPHOLOGY OP CRANIAL MUSCLES IN SOME VERTEBRATES. 2 0 1

external (Acipenser), grows up to the skull. In Sauropsidanembryos the depressor palpebrse inferioris is given off fromthe anterior margin of the levator maxillse superioris, whichbecomes inserted into the palato-quadrate—this is preservedin birds, whereas in reptiles various changes, modifications

TEXT-PIG. 28.

2 8 .

Text-figs. 28-33.—Amia, embryo 8A mm. Text-fig. 2S is the mostanterior.

or atrophy, occur; and the adductor mandibulse divides intoexternal and internal portions, of which the former grows upto the skull, whilst the primitive origin of the latter wasprobably to the palato-quadrate and the hind end of thepalato-pterygoid bar—this is preserved in Chelonia, but isvariously modified in other groups (loc. cit .) .

A comparison of the various forms of the intermandibularis

202 H. KDGEWOKTH.

shows that its primitive condition is that of a transversesheet passing from one rainus of the lower jaw to the other.This exists only in Salnio. In Necterus, Triton, Ceratodus,Scyllium, Acanthias, Polypterus, Lepidosteus, and Amiait extends backwards, underlying the fore part of the inter-

TEXT-FIG. 29.

2 9 .

hyoideus, and in Amia and Triton, it divides into anteriorand posterior portions. In Atiuran larvae it divides intosubmentalis, rnandibulo-labialis and submaxillaris, of whichthe first has a special relationship to the inferior labialcartilages. In Sauropsida it forms a continuous sheet withthe interhyoideus and C3vd. In Lepus it is overlapped bythe forward-growing interhyoideus.

MORPHOLOGY OF CRANIAL MUSCLES IN SOME VERTEBRATES. 2 0 3

The intermandibularis, in correlation with its developmentin the mandibular segment, is usually innervated by the Vthcranial nerve. Vetter, however, found that in Scyllium andPrionodon the portion immediately behind the symphysis ofthe jaws was innervated by the Vth, and the greater portion

TEXT-FIG. 30.

30.

of the muscle by the Vllth, and that in Acanthias, Heptsm-chus, and Scymnus the whole of the muscle was innervatedby the Vllth. He concluded that in the former the greaterpart, and in the latter the whole, of the intermandibularis(Csv^ had disappeared, and had been replaced by the inter-hyoideus (Csv2), which had gained a secondary insertion intothe lower jaw. But this opinion, which was founded on adulfc

204 !•'. H. EDGEWORTK.

anatomy only, is at variance with the phenomena of develop-ment ; both in Scyllium and Acanthias a well-marked inter-mandibularis is formed in the mandibular segment, andspreads back below the interhyoideus and fusing with it behindthe hyoid bai\ Its partial or total innervation by the Vllthmust consequently be a secondary phenomenon.

TEXT-FIG

31.

The intermandibularis of Ceratodus is also innervated bythe Vllth (Ruge), and its hinder part in Triton (Driiner).

Ruge held that what is here called the intermandibularis isa facial muscle, and that its innervation from the Vth issecondary, but in Ceratodus, as in all the vertebrates examined,it is developed in the mandibular segment. Ruge's theorywas based on the idea that " Es liegt auch nicht der geringste

TEXT-FIG. 32.

t ^ ,

U&v*

33.

206 1<\ H. EDGEWORTH.

Gruud vor nra an der Ursprnnglichkeit der Einrichtungeu beiden jSTotidaniden zu zweifeln." Study of the comparativeembryology of the cranial muscles, however, leads to consider-able doubt on this matter.

HYOID MUSCLES.

Iu Scyllium the ventral end of the hyoid myotome becomescontinuous with the Jateral edge of the future interliyoideusin 14 mm. embryos. In 16 mm. embryos the formation ofthe hyoid bar begins by aggregation of the mesoblast cells,forming a pro-cartilaginous, tract lateral to the alimentarycanal, and the myotome is at first partly continuous with theiuterhyoideus, partly inserted into the upper end of the bar(Text-figs. 5 and 6), forming a levator hyoidei. In 17 mm.embryos the hyoid bar extends upwards towards the auditorycapsule (Text-fig. 7), partly covered by the myotome, which isinserted into its lateral surface (C3hd of Ruge). It is onlylater, in embryos between the lengths of 23'and 30 mm., thatthe hyoid bar separates into ceratohyal and hyomaudibula, asin Acanthi as (Gaupp). The continuity of the myotome andthe interhyoideus becomes lost, and the lateral edge of thelatter is inserted into the ceratohyal. In 23 mm. embryos(Text-figs. 12, 13, cf. Text-figs. 10 and 11) backward extensionof the myotome and interliyoideus takes place, so that a con-tinuous dorso-ventral sheet (C3vd of Ruge) is formed behindthe hyoid bar. Later on, in 40 mm. embryos, the myotomeextends forwards, completely covering the hyomandibularcartilage, and its anterior edge is inserted into the quadrate.

In the Teleostoini the relations of the fore part of thehyoid myotome (retractor or adductor mandibulte) to thehyomandibular cartilage are different from those existing inSelachii. The retractor of Acipenser is inserted into itshinder edge, and of Polypterus into its inner surface, and tbeadductor of Lepidosteus, Amia, and Salmo is inserted intoits inner surface. Further, the Vllth nerve (hyoid branchof Vll th in Polypterus) winds round the cartilage iu

MORPHOLOGY OP CRANIAL MUSCLES IN SOME VERTEBRATES. 2 0 7

Acipenser and Polypterus, pierces it in Lepidosteus, Amia,and Salmo.

The development is not yet known in Polypterus. In tliefirst stages, hitherto described, of Acipenser ruthenus(Parker), Lepidosteus (Parker), and Salmo trut ta (Stohr),the hyomandibula is stated to abut against the auditorycapsule. Rutherford1 states that in the brown trout a down-growth of no great size, from the periotic capsule at the edge

TEXT-FIG. 34

3 4 .

Amia, embryo 10mm., transverse section.

of the feuestra ovalis, joins with the symplecticum in front ofthe Vll th nerve, and finally unites with the primitive hyo-mandibula.

In 8 mm. embryos of Acipenser the hyoid bar, in a pro-cartilaginous condition and nnsegmented, does not extend upto the auditory capsule. The 'Vllth nerve passes over theupper end of the bar, and then downwards outside it (Text-fig. 19). In 8 | mm. embryos the hyoid bar extends up towards

1 The paper is as yet only published in abstract.

20S !•'. H. KJXitiWOK'L'H.

TEXT-FIG. 35.

COX W i u i . . 3 6.Texfc-figs. 35-37.—Polypterus, larva 7i cm. Text-fig. 35 is fclie

most anterior.


tlie auditory capsule and in front of, and outside, the V l l t hnerve, which now winds round it (Text-figs. 20 and 21). Thehyo-mandibnlar cartilage is formed in part from the upperportion of the bar present in 8 mm. embryos, and in partfrom the upward extension. The hyoid muscles in 8 mm.embryos consist of a hyoid myotome, the anterior part ofwhich is inserted into the upper end of the hyoid bar (Text-

TEXT-FIG. 37.

37.

fig. .19), forming a levatov hyoidei, and the posterior part ofwhich forms a dorso-ventral sheet—homologous with Covd ofSelachians—continuous with the posterior part of the inter-hyoidens (Text-fig. 21), whilst the anterior part of the inter-hyoideus is inserted laterally into the hyoid bar.

The sequence oE events in the other Teleostomi examinedis similar to that occurring in Acipenser, the upgrowth ofthe hyoid bar to the auditory capsule taking place in 8 mm.embryos of Lepidosteus, 6£ mm. embryos of Amia, and 5 - mm.embryos of Sa lmo f a r io . In no case was any downgrowth

210 F. H. EDGEWOETH.

from the periotic capsule found. In Lepidosteus, Ainia, andSalmo, the Vll th nerve, at first winding round the hyoidbar, subsequently pierces the hyomandibula owing to chon-drification spreading round i t ; the more primitive conditionis preserved in Acipenser and Polypterus.

The adult condition of the hyoid muscles in these Teleostomiis not quite uniform. In all the dorso-ventral sheet C3vddivides into dorsal and ventral portions. In Polypterus theanterior and posterior portions of the myotoine do not separatefrom each other, but form one muscle, the retractor hyomaudi-bularis et opercularis. In the others separation takes place;the anterior part, i . e . the original levafcor hyoidei, forms aretractor hyomandibularis in Acipeuser, and an adductorhyomandibularis in Lepidosteus, Amia, and Salmo. Theposterior part, i. e. the upper part of C3vd, forms a M.opercularis in Acipenser and Lepidosteus, an adductor andlevator operculi in Amia and Salmo. Iu 9i mm. embryos ofSalmo the adductor mandibularis additionally spreads forwards,forming the adductor arcus palatini.

The fore part of the interhyoideus of Acipenser forms thehyoideus inferior (Cs5 of Vetter), the hinder part, i .e . thelower part of C3vd, forms a constrictor operculi (Cs3 and Cs4

of Vetter). In Polypterus the condition is similar.1 In Lepi-dosteus, Amia, aud Salmo, the fore part forms the hyoideusinferior; the hinder part becomes attached laterally to thehyoid bar (only partially so in Lepidosteus), and forms thehyoideus superior. The median raphe of these muscles ispreserved iu Acipenser, Lepidosteus, and Polypterus; inSalmo aud Amia it is lost, and the hyoideus inferior becomesattached to the hypohyals of the same and opposite side.

In 8^ mm. embryos of Amia the Aulage of the hyomaxillaris3

muscle becomes separated froni the upper edge of the hyo-hyoideus inferior (Text-fig. 29); it grows forward to Meckel's

1 Intermaxillaiis posterior and mantle muscle of Pollard.2 Superior deeper portion of the genio-hyoid of Allis. A different

terminology is used in this paper, as the word ''genio-liyoid" is generallyused to denote the anterior element of the hypohranchial spinal muscles.

MORPHOLOGY OF CRANIAL MUSCL10S IN SOME VEETKHKATES. 211

TEXT-FIG. 38.

3 8 .

TEXT-PIG. 39.

hU\J\u id.

3 9 .Text-figs. 38 and 39.—Ceratodus, embryo stage 40; transverse

sections. Text-fig. 38 is the more anterior; the left side ofthe sections is slightly anterior to the right.

212 P. H. EDGEWORTH.

cartilage dorsal to the intermandibularis posterior. A similarmuscle is formed in Salmo; it gi'ows forward ventral to theinter-mandibulaiis. In 9£ mm. embryos of Lepidosteus and9 mm. embryos of Acipenser (Text-fig. 2 2 A) a similar Anlageis formed from the dorsal edge of the hyoideus inferior or CsB

and develops into the hyomaxillaris ligament.1 In Polypterus,? species, Pollard described, but did not name, a small muscle

TEXT-FIG. 40.

l.XWJJ.

40.Text-fig. 40.—Ceratodus, stage 40, longitudinal horizontal section.

" at the angle of the jaw in the substance of the ligamentwhich binds the hyomandibula quadrate and stylohyal,"innervated by the opercular branch of the hyoid branch ofthe VIIth. In P o l y p t e r u s s enega lu s only a ligament ispresent.

In Ceratodus, between the stages oE 38 and 40, the hyoidmyotoine and interhyoideus spread backward in the opercular

1 Mandibnlo-hyoid ligament of van Wijhe.

MORPHOLOGY OF CEANIAL MUSCLES IN SOME VERTEBRATES. 213

fold (Text-fig. 40), and form in the latter stage (Text-fig. 38)anteriorly a levator hyoidei inserted into the upper end of thehyoid bar, and an interhyoideus, and posteriorly a continuousventro-dorsal sheet C2vd in the operculnm. In stage 42 theAnlage of the hyomaxillaris ligament is cut off from theupper edge of the interhyoideus and spreads forwards to thehind end of Meckel's cartilage (Text-fig. 41). In stage 42(Text-fig. 41) the hyoid bar extends upwards and inwardstowards the under surface of the pro-cartilaginous tract con-necting the parachordal plate •with the auditory capsule,forming the hyomandibula, the original hyoid bar formingthe ceratohyal and hypohyal.

The upper part of the originally pro-cartilaginous hyoman-dibula chondrifies; the lower forms a fibrous tract connectingits outer end with the upper end of the ceratohyal (Text-fig.50). In stage 48 a downgrowth occurs from the outer edgeof the auditory capsule, external to the hyomandibular branchof the Vl l th (Text-fig. 47), and becomes separated, forming acartilage abutting against the outer end of the hyomandibula(Text-fig. 50), and a second more dorsally situated piece issubsequently cutoff from the auditory capsule (Text-fig. 50).1

The insertion of the levator hyoidei into the upper end of theceratohyal is preserved in the oldest embryo examined, butis not present in the adult (Ruge) ; it is, however, retained inProtopterus (vide description by Ruge).

In Necturus Miss Platt stated that the "hyoid mesothelialt issue" (here interpreted as "myotome") divided into adorsal digastricus, which " i s ultimately connected with theposterior extremity of the rnandibular bar by a long tendon"

1 This description of the hyomandibula coincides with and amplifiesthat of K. Fiirbringer. The cartilage (or cartilages) cut off from theauditory capsule is probably, from its relation to the hyomandibnlarlivanch of the Vllth, that described by Huxley, Ridewood, Ruge, andSewertzoff as the "hyomandibula." From the descriptions given itwould appear probable that no part of a true hyomandibula is preservedin the adult, and that (vide Ridewood) the cartilages cut off from theauditory capsule are variable.

214 F. H. BDGEWOETH.

TEXT-PIG. 41.

"a

4 2 ,

Text-figs. 41-43.—Ceratodus, embryo stage 42 ; transverse sec-tions. Text-fig. 41 is the most anterior ; the left side of tliesections is slightly anterior to the right side.

MORPHOLOGY OF CllANIAL MUSCLES IN SOME VERTEBRATES. 215

and a ventral ceratohyoideus externus. Examination ofsections of 14^ mm. embryos shows that there is a stage inwhich the future digastricus (the " cephalo-dorso-niandi-bularis " of Driiner) forms a levator hyoidei, inserted into theupper end of the hyoid bar, whilst below the cerato-hyoideusexternus the Anlage of the hyomaxillaris ligament is formed(Text-fig. 55).

TEXT-FIG. 43.

4 3 .

It is of interest to note that in Siren (Driiner) there is alevator hyoidei, a slip of the cephalo-dorso-mandibularis,i. e. in thab animal the primary insertion of the muscle is notwliolly lost.

The interhyoideus1 of Necturus spreads backward behindthe hyoid bar in the opercular fold, and this posterior part,at first entirely ventral, spreads upwards laterally external tothe cerato-hyoideus externus and depressor mandibulas. Thereis a similar development oE the interhyoideus in Triton, and

1 Posterior mylohyoid of Mivai-t and Miss Platt.VOL. 5 6 , PART 2 . NEW SEE1ES. 16

216 V. H. EDGEWORTB.

the hinder part gains an attachment to the first branchialbar.1

Schultze described the hyoid muscles of the larvee ofPelobates fuscus as consisting of an orbito-hyoideus, sus-pensorio-hyoideus, cerato- hyo-angulnris, quadrato-angularis,

TEXT-FIG. 44.

44-.

Text-figs. 44 and 45.—Ceratodus, embryo stage 46 ; longitudinalhorizontal sections. Text-fig. 44 is the more dorsal; the leftside of the sections is slightly dorsal to the right side.

mid suspensorio-angularis. In Kaua the myotome of thehyoid segment separates from the interhyoideus in 6 mm.embryos. It divides in 7 mm. embryos into an upper and lowerportion (Text-fig. 58); the former develops into the orbito-hyoideus, which passes from the processos niuscularis of the

1 First interbranchial of Driiner.

MOliPHO.LOG\r OF CRANIAL MUSCLES IN SOME VERTEBRATES. 217

palato-quadrate to the ceratoliyal; the latter, which is thehyomaxillaris, grows forwards to the outer end of Meckel'scartilage and divides into the cerato-hyo-angularis, snspen-sorio-angularis, and the quadrato-angularis (Text-fig. 59). InBufo l e n t i g i n o s u s the upper portion of the myotome formsonly an orbito-hyoideus, as inEana; in Pelobates and Alytes itforms an orbito-hyoideus and suspensorio-hyoideus. In Pelo-

TEXT-ITO. 45.

4 5 .

bates and Bufo l e n t i g i n o s u s the hyo-maxillaris dividesinto three muscles as in Rana, in Alytes into two only, thecerato-hyo-angulai'is and quadrato-anguLiris (Text-fig. 63).

In Rana, at metamorphosis, the upper end of the orbito-hyoideus extends upwards on the atrophy of the processusmuscularis of the palato-quadrate; subsequently, on rotationbackward oE the palato-quadrate, the lower end of theorbito-1 The coraco-niandibulavis in this drawing is unfortunately not named.


TEXT-FIG. 46.

46

TEXT-PIG. 47.

Ivj.m^.

M. m&uj

COV.Ujoul

Text-figs. 46-48.—Ceratodus, embryo stage 48. Text-fig. 46 ithe most anterior.

MORPHOLOGY OP CHANTAL MUSCLES IN SOMU VERTEBRATES. 219

hyoideus gains a new insertion to the hind end of the lowerjaw. The cerato-hyo-angularis, suspensorio-angularis, andquadrato-angularis assume a more vertical position on therotation of the palato-quadrate, and form the inner portion,whilst the original orbito-hyoideus forms the outer portion,of the depressor mandibulje.

The interhyoideus of thelarvse of Rana1 forms a transverseband connecting together the two ceratohyals (Text-fig. 57),and this is also the case in Alytes. In Pelobates and Bufo

TEXT-F i

l e n t i g i n o s u s it extends backwards below the branchialcavity, and this hinder part forms the snb-branchialis (ofSchultze), and the diaphragmato-branchialis (of Schultze) isseparated from the median edge of this muscle.

The digastric muscle3 of Mammals is either monogastric(digastricus spurius), inserted into the jaw, or digastric(digastricus verus), with a tendon between the two bellieswhich may or may not be connected with the hyoid bone.

1 Subhyoideus of Ecker and Gaup, and of Schultze.5 This bare outline only is given, as the matter has been so thoroughly

discnssed by Bijvoet.

220 F. H. EDGBWORTH.

The anterior belly of a digastricus verus is innervated by theVth, the posterior belly by the Vllfch. A digastricusspurius has a deeper or superficial tendinous inscription,and is also innervated by both Vth and VHth.

Anatomists who have investigated the adult conditions of;the muscle have expressed various views as to its origin;some, e. g. His and Chaine, thought that the muscle wasdeveloped from one mass; others, e. g. Humphrey, Gegen-bauer, Ruge, Fiirbringer, Bijvoet, have held that it wasdeveloped from two masses.

Bijvoet, the latest investigator of the subject, was of opinionthat the condition present in Monotremes—a M. depressormandibulaa anterior, and a M. stylohyoideus—is the " Aus-gangsform," that from this was developed a digastricusverus, and that a digastricus spurius was a secondai-y con-dition. He was also of opinion that a M. intermandibularisseparated into a M. mylohyoideus and a M. depressormandibute anterior. The only descriptions of the develop-ment of the digastric muscle which have hitherto been givenare those by Futamura of human and pig embryos. He saysthat the common Anlage of the digastricus, stylohyoideus,and stapedius is visible in twenty-seven to thirty day humanembryos as a " medialwiirts sich anhiiufende dicht gedriuigteMuskelblastemgewebe," which is continuous laterally with theplatysma Anlage, the whole foraiing a single mass. In embryosa little older the platysma and digastric Anlagen separate. Insix weeks' embryos the digastric Anlage passes forward to theanterior border of the lower jaw. The mylohyoid nerve at thisdate passes to the mylohyoid muscle only; it does not innervatethe anterior belly of the digastric until the age of seven weeks.The stylohyoid and stapedius begin to separate from theposterior belly of the digastric at the age of six weeks. Thedigastric is thus solely a facial muscle, the anterior part of whichreceives a secondary itmervatiou from the trigeminal nerve.

Bijvoet doubted this account given by Futamura, as itappeared to him to disagree with the results of comparativeanatomy.

MORPHOLOGY OF CRANIAL MTJSCT/ES IN SOMK VMR'i'EBBATBS. 221

Fu tamura ' s account of the development, o£ the facial andplatysnia muscles is tha t their Anlage separates, as s ta tedabove, from the outer aspect of the common facial A n l a g e ;in thir ty-one to thirty-four day embryos it spreads aborallyalmost to the shoulder region., forming the platystna colli, andin six-week embryos also forwards, in two directions sepa-rated by the outer ear, forming a platysina occipitalis and a.facial portion. The lat ter passes forwards over the edge ofthe lower jaw to the forehead, eyelid, upper lip, and temporalregion, separat ing into a deep and a superficial layer.

In 3 mm. embryos of the rabbi t the hyoid myotome is con-tinuous below with the epithelium lining the hyoid section ofthe cephalic coelom (Text-fig. 77). I n 4 mm. embryos thewalls of the cephalic ccelorn have come together , and theAnlage of the interhyoideus is formed from its epithelial w a l l ;eacli half is continuous laterally with the lower end of themyotome (Text-fig. 81). I n 7h mm. embryos the myotome ispartially separated into an upper and a lower p a r t ; the formeris the Anlage of the posterior digastric, stylohyoid, and stape-dius, the la t ter tha t of the anterior digastric (Text-fig. 89). In.embryos between 8 and 9 mm. the hyoid bar is formed,1 andin its whole extent simultaneously, so tha t there is no s tagein which the Anlage of the posterior digastr ic , stylohyoid, .andstapedius is inserted into the upper end of a hyoid bar whichhas not yet extended up to the auditory capsule. In 9 mm.embryos (Text-figs. 92 and 93) the lateral edge of the inter-

' The ''body of the liyoid" in tlie rabbit is formed from the ventralends of the liyoid and first branchial bars. No basihyal nor basi-brancliial is developed. In 9 and 13 mm. embryos a column of cells—the remains of the glosso-tbyroid duct—extends downwards from theforamen ctecvmi in the middle line between the hyoid nnd first branchialbars. Antero-posterior fusion of the ventral ends of these bars to formthe body of the hyoid, and the commencement of formation of a jointbetween tlie body and the first branchial cornua, take place in embryosbetween the stages of 13 and 17 mm. Ohondrification takes place laterin the "body" than in the liyoid and first branchial cornna. Thesefindings confirm the suggestions of Parsons; in the rabbit, however,there is no basihyal.

222 T. H. EDGEWOE'l'H.

hyoideus has separated from and extended upwards outside theanterior digastric, which has grown a little forwards. In 10mm. embryos the anterior end of the anterior digastric hasreached Meckel's cartilage, the interhyoideus has extendedforwards, and also backwards in the neck forming the platysinacolli, and the stapedius has separated from the Anlage oi theposterior digastric and stylohyoid. In 13 mm. embryos theAulage of the posterior digastric and stylohyoid has separatedinto those muscles, and the lateral edge of the fore part of theinterhyoideus (Text-fig. 96) has extended upwards and for-

TEXT-FIG. 49.

4 9 .Text-fig. 49.—Cevatodus, embryo 15 mm.; portion of transverse

section taken between the fifth branchial segment and the lung.

wards forming the platysma occipitalis and platysma faciei.The posterior digastric forms a tendon (vide Krause).

There is thus in the rabbit a stage'of development prior tothe first described in man by Futarnura, in which the Anlageof the platysma faciei, platysma occipitalis, and platysmacolli is a structure homologous with the interhyoideus of lowerforms. The anterior digastric is homologous with the byo-lnaxillaris of some Amphibia and Teleostomi.

The Homolog ie s of t h e Hyoid Muscles.—In Alytes,Bufo, Rana, Pelobates, aud Lepus, the lower end of the hyoidmyotome becomes separated from the part above and formsa longitudinal muscle—the hyo-maxillaris—connecting thehyoid bar with the lower jaw. An homologous muscle is

OF 0BAN1AL MUSCLES IN SOME VEK.TEBKATKS. 223

formed iu Ami a and Salnio, but differs in that it is separated'from the upper end of the hyoideus inferior. The first men-tioned method of formation is probably the primitive one,for serially homologous muscles, interarcuales ventrales, areformed from the lower ends of branchial myotomes wherethere are no muscles homologous with the interhyoideus;the method of formation in these Teleostomi is probablyrelated to the secondary position of the adductor hyoinandi-bnlaris internal to the upper part of the hyoid bar. InUrodela (Necturus, Triton), Ceratodus, Lepidosteus, and

TEXT-FIG. 50.

50.Text-fig. SO.—Ceratodus, advanced embryo, length ?; portion of

transverse section, to show relations of the hyoniundibularcartilage.

Acipetiser a corresponding Anlage develops into a hj'o-maxillaris ligament. In SeJachii (Scyllium, Acanthias) andiu Sauropsida no hyo-niaxillaris Anlage is formed.

The developmental history of the hyo-inaxillaiis suggeststhat its primitive condition was that of a longitudinal musclepassing from the hyoid bar to the hind end of Meckel's carti-lage, but this is not preserved in any of the animals investi-gated. In Teleostomi (Aniia and Salnio) the front end of themuscle extends forwards along Meckel's cartilage.

In Chimsera there is a similar muscle (hyoideus inferior ofVetter) extending from the hyoid bar along the lower jaw.

224 T. H. EDGEWOBTH.

In Rana, at metamorphosis, the muscle becomes morevertical in position, and forms, with the orbito-hyoideus, thedepressor mandibulae ; this stage is preceded by a larval one,in which the muscle, having a longitudinal direction, is in partattached to the palato-quadrate bar. In Mammals the hyo-uiaxillaris (anterior digastric) may lose its attachment to thehyoid b;ir and form part of a digastricus verus with a tendonnot attached to the hyoid bar, or part of a digastricus spurius.

The part of the hyoid myotome above the hyo-maxillarisin cases where this is formed, or above this and the cerato-hyoideus externus (in the Urodela), or the whole myotome,where either or both of these muscles is not formed, is at firstwholly or partially (Scyllium) inserted into the upper end ofa liyoid bar, which has, or has not yet, extended up to theauditory capsule, forming a levator hyoidei. This holds forScyIlium, Acipenser, Lepidosteus, Amia, Salmo, Ceratodus,Necturus, Triton, Raua, and other Anuran larvaa, Chrysemys,and Gallus. In the Amphibia the hyoid bar remains in thisprimitive condition, in the other groups it extends upwardsto the auditory capsule.

According to Kingsbury and Reed, the columella auris of:Urodela is the homologue of the hyomandibula of otherforms. If this be so, its dorsal relation to the seventh nervewould suggest that, it is homologous with the hyomandibulaof Teleostei, where a similar relation holds, rather than withthat of Selachii, Ceratodus, and Sauropsida, which lies ventraLto the Vllfch.

Against such homology, however, it might be urged that inScyllium, Acipenser, Lepidosteus, Amia, Salmo, Ceratodus,Clirysemys, and Gallus (Geoffry Smith), the hyomandibulais formed by a secondary segmentation occurring in a hyoidbar, which extends continuously up to the auditory capsule,whereas this is not stated by Kingsbury and Reed to occur inUrodela.

A levatof hyoidei—attached to the upper end of a hyoidbar—is not preserved to adult life in any of the animalsexamined. In Urodela and Sauropsida it extends downwards

MORPHOLOGY OV CUANIAL MUSCLES IN SOME VERTEBRATES. 225

TEXT-FIG. 52.

IV/.tvu)

s|>.h\..Alv

5 2 .

Text-figs. 51 and 52.—Necturus, embryo 12 mm. Text-fig. 51is the more anterior.


to Meckel's cartilage, foraiing the depressor inandibulas. InRana this also occurs at metamorphosis, the muscle formingthe outer part of the depressor mandibula3. In ScyIlium thelevator hyoidei, on the upgrowth of the hyoid bar, is insertedinto its outer surface, and in very late stages of developmentextends forwards to the quadrate. In Teleostoini, on the up-growth of the hyoid bar, the levator hyoidei becomes insertedinto its posterior edge or inner surface, and in Salmoadditionally spreads forward to the palato-quadrate. InCeratodus the insertion of the levator hyoidei to the upperend of the ceratohyal is lost, but it is preserved in Protopterus(vide description by Ruge). In Lepus there is no stage indevelopment in which there is a levator hyoidei inserted intothe npper end of a hyoid bar, for this is formed simultaneouslyin its whole length, but the portion of the myotome above theAnlage of the hyo-maxillaris (anterior digastric) is a mass,which is homologous with the levator hyoidei of other forms,and lies outside the hyoid bar; it subsequently divides intostnpedius, stylohyoideus and digastricus posterior. It ishomologous with the M. styloideus of Monotremes. Theupper end of the levator hyoidei is attached to the auditorycapsule; this attachment, in Anura, is preceded by a larvalstage, in which the upper end ot the muscle takes originfrom the processus musculan's of the palato-quadrate bar.

The primary form of the interhyoideus—formed from thewalls of the obliterated hyoid section of the cephalic cceloin,and serially homologous with the iutermandibularis—wouldappear to have been a transverse band connecting the twohyoid bars, but in all forms examined, other than liana andAlytes, it extends backwards. In Urodela, Anura, andrabbit there is a backward extension of the interhyoideusonly, but in Selachii, Teleostoini, Ceratodus, and Sauropsida,of both myotome and interhyoideus, forming a continuousventro-dorsal sheet (C2vd of Ruge) behind the hyoid bar.The backward extension of the interhyoideus, or of this andof the myotome, takes place in the opercular fold in Urodela,Anura, Ceratodus, and Teleostomi; in part in the opercular

MORPHOLOGY OP CKAJVIAT, MUSOLES JN SOME VERTEBRATES. 227

TEXT-PIG. 53.

jitt. tiv.An.

54.

Text-figs. 53 and 54.—Necturns, embryo 13 mm., tiunsversesection. Text-fig. 53 through tbe fourth branchial segment,Text'fig. 54 a little more posterior.

228 P. H. EDGUWORTH.

fold (only existing ventrally) in Sauropsida and rabbit; andin Scyllium entirely in the wall of the head, no opereular fold,even as an atrophying Anlage, being developed.

The backward extension of the interhyoideus forms thehinder part of the interhyoideus of Urodela, and the snb-brauchialis of Anura. In the rabbit the attachment of theinterhyoideus to the hyoid bar is lost, and it spreads downthe neck, forming the plafcysma, and also upwards audforwards, forming the superficial occipital and facial muscles.

O3vd persists as a continuous ventro-dorsal sheet inScyllium, Ceratodus, and Sauropsida ; in the latter group, incorrelation with tlie atrophy of the gill-clefts, it spreadsbackwards in the neck, forming the constrictor colli; inTeleostomi it separates into dorsal and ventral portions, theformer developing into the opereular muscle or muscles, thelatter into a constrictor operculi (Acipenser and Polypterus),or hyohyoideus superior (Lepidosteus, Amia, Salmo).

The hinder part of the interhyoideus of Urodela and theplatysma of the rabbit imitate, to some extent, the constrictorcolli of Sauropsida, but this is due to a dorsal extension oftheir lateral edges over the hyoid myotome after theirformation from the interhyoideus only.

It will be showUj later, that the probable primitive con-dition of the muscles of each branchial arch was, a M. levator,a M. marginalis, a M. interarcualis, and a M. transversnsventralis. The levator liyoidei is serially homolog-ous withthe first, and the hyo-maxillaris with the third of these. Thecerato-hyoideus externus is serially homologous with the Mm.marginales and their homologues the Anlagen of the gill-muscles, aud may possibly be derived from a hyoidean M.marginalis, but there is no trace of such a muscle in othergroups. There are no homologues of the transversi ventialesin the mandibular and hyoid segments.

The primitive condition of the mandibular and hyoidmuscles was probably one in which the former lay wholly infront of the latter. This condition exists in the embryo butdoes not persist; during development, in correlation with the

MOEPHOLOGY OF CRANIAL MUSCLES IN SO 1111 VERTEBRATES. 229

TEXT-FIG. 55.

Text-figs. 55 and 56.—Necturus, embryo 14*. mm., transversesections. Text-fig. 55 through the hyoid segment, Text-fig. 56through the fourth branchial segment.

230 F. H. BDGI5WORTH.

increase in size of the jaws, there is a gradual overlapping" ofthe hyoid bar by the mandibular skeletal structures, withassociated secondary changes in the muscles. Thus, thelevator hyoides shifts its insertion from the hyoid bar to thehind end of Meckel's cartilage iu Amphibia and Sauropsida,and the intermandibularis partially underlies the interhyoi-deus in Selachii, Teleostomi, Ceratodus, and Urodela. It isprobably in connecDion with this overlapping that the hyo-raaxillaris Anlage becomes a ligament in Urodela, Cera-todus, and some Teleostomi, and is not developed inSelachii and Sauropsida.

EYE MUSCLES OP THE RABBIT.

The development of the external ocular muscles in Teleo-stoman and Amphibian embryos was not followed.

In pig embryos of 10 mm. maximum and 6 mm. Nacken-lange, Reuter found the Anlage of the eye muscles as an" untrenubarer Zellcornplex/' which, lie held, " als Anhau-fung von morphologisch urspriinglich Keimzellen aus demMesenchym hervorgeht."

In 3 ram. embryos of the rabbit the premandibular Anlageis developed, on each side, as a hollow outgrowth of the foreend of the alimentary canal (Text-fig. 75). This outgrowthbecomes solid by proliferation of its walls as it is constrictedoff, and iu 3^ mm. embryos (Text-fig. 79) it forms a solid massconnected with its fellow by a solid string of cells lying acrossthe fore end of the alimentary canal just below the anteriordown-turned end of the notochord. The connecting stringof cells has disappeared in 4 - mm. embryos. The premandi-bular Anlage forms a crescent-shaped mass in 4 mm. embryos(Text-fig. 84); and from this the recti superior, inferior,interims, and obliquus inferior are formed (Text-figs. 96, 97).The obliquus superior is formed from the anterior extremityof the upper end of the mandibnlar myotome in 3^ mm.embryos (Text-fig. 7S). The development of the abducensAnlage is doubtful; in 3^ mm. embryos it is visible lying

MORPHOLOGY O.F CRANIAL MUSCLES IN SOME VERTEBRATES. 2 3 1

behind the premandibular Anlage and internal to the man-dibular myotome (Text-fig. 79). In 2£ mm. embryos itapparently is represented by a group of cells lying abovethe first gill-cleft and continuous behind with cells lying inthe hyoid segment—cells which in 3 mm. embiyos have diffe-rentiated into myotome and surrounding mesoblast. It isprobable, therefore, that the abducens Anlage is formed fromthe mesoblast of the hyoid segment before the myotome is

TEXT-FIG. 57.

J.Wmi(. not, i

57.

Rana, embryo 6 mm., longitudinal vertical section.

formed. The abducens Anlage begins to separate into rectusexternus arid retractor oculi in 13 mm. embryos (Text-fig. 96).

These observations suggest that perhaps in pig embryos ofa younger age than those investigated by Reuter a similarseries of events may occur. In the later stages of develop-ment there is also a difference between the pig and therabbit; in the former, according to Reuter, the retractor oculiis formed from all four recti, in the latter it is formed fromthe abducens Anlage only, as is usual in Vertebrates.

VOL. 5 6 , PART 2 . NEW SERIES. ]7

232 F. H. EDGEWOItTH.

BRANCHIAL MUSCLES.

The homologies between the branchial muscles of variousvertebrates are obscured by the absence of uniformity innomenclature. The word "interbrancbial " has been appliedto many quite different muscles. It was used by Vetter todenote the layer of muscle-fibres -which lies external to thebranchial bars and internal to the superficial constrictor inSelachii. I t was subsequently employed by Bronn and bySchultze to denote longitudinal muscles between the ventralends of branchial bars in Amphibia; by Driiner, to denotetransverse muscles in Amphibia ; by K. Fiirbringer and byGreil to denote slender vertical muscles in Cemtodus.

In this paper the word "interbranchial" is used exclusivelyin the Selachii in the sense of Vetter; longitudinal musclesbetween the ventral ends of branchial bars are called " inter-arcuales ventrales " (vide i n f r a ) ; transverse muscles arecalled " transversi ventrales," and the vertical muscles ofCeratodus are called Mm. margiuales, as they are exactlyhomologous with the Mm. marginales of Anuian larvtedescribed by Schultze.

Fiirbringer included two sets of muscles under the term" hypobranchial spiinil musculature"1—(1) Those which aresometimes called ventral longitudinal muscles, e .g. cora-co-mandibnlaris, coraco - hyoideus, genio - hyoideus, sterno-hyoideus; (2) the coraco-branchiales of Elasmobranchs,Teleostoini, and Dipnoi.

Investigation of the development of these muscles, how-ever, shows that whereas the ventral longitudinal musclesare derived from trunk-myotomes, the coraco-branchialesare derived from the ventral end of one or more branchialmyotomes, i . e . are of cranial origin. The above-mentionedterminology would therefore appear to be in need of revision,

1 The name " hypoglossal musculature " employed by Neal and byCorning has nearly, but not quite, the same meaning as Fiirbringer's" hypobrancnial spinal musculature," e.g., it would include the cerato-hyoideus (intevai'cualis venti-alis I) of Sphenodon.

MORPHOLOGY Off CRANIAL MOSCM3S IN SOME VJBETJ3BBATKS. 2 3 3

and in this paper longitudinal muscles derived from trunk-rayotomes arc called " hypobraticliial spinal muscles," andlongitudinal muscles derived from branchial myotomes arecalled " hypobranchial cranial muscles."

The Anlagen, which ia some Vertebrates grow backwardsand form coraco-branchiales, are homologous with Anlagenin other Vertebrates, which form muscles passing betweenthe ventral ends of the branchial bars. Many different

TEXT-FIG. 5S.

5 8 .

Rana, embryo 7mm., transverse section.

names have been given to the latter muscles, e.g. inter-branchiales s. constrictores arcuum branchialium (Bronu),constrictores arcuum (Mivart), interbranchiales (Schultze),subarcuales (Driiner).

Vetter called certain muscles in the branchial arches ofAcipenser " iuterarcuales ventrales," and gave the name of"obliqui ventrales" to exactly homologous muscles inTeleostei. One or other term is superfluous, and followingAllis, that of "obliqui ventrales" is used in this paper fortheTeleostomi generally. The name "interarcuales ventrales"

234 P. H. EDGEWO.RTH.

is used for the longitudinal muscles passing between theventral ends of the branchial bars.

The foremost lf interarcualis ventralis" passing from thefirst branchial to the hyoid bar has received many names,e. g. ceratoidien lateral on petit ceratoidien (Cuvier), inter-cornalis (Owen), cerato-hyoidens interims (Furbringer, MissPlatt, Driiner), cerato-hyoideus (Osawa), hyoideus lateralis(Bendz), kerato-byoideus (Bllenberger and Baum), inter-hyoideus (Dnbois), kerato-fchyro-hyoideus (Jaquet). Thename "branchio-hyoideus" was applied to this muscle inSphenodon (loc. cit .) , and is employed in the case of otheranimals, when it occurs, in this paper.

In Scyllium, van Wijhe desci-ibed the coraco-branchialisand coraco-mandibularis as developing from the walls of theobliterated anterior prolongation of the pericardium, andfrom " Nebenzweige," given off from the " Unterenden derWande der Visceralbogeuhohlen."

I t will be shown later (p. 268) that the coraco-mandibularisand coraco-hyoideus are developed from the fourth to eighthtrunk-myotomes. The five bi'anchial myotomes form at firstepithelium-lined cavities continuous below with the cephalicccelom (Text-fig. 2). They separate from the cephalic coelomin 14 mm. embryos, and their cavities become obliterated(Text-fig. 4). In 17 mm. embryos the lower ends of thebranchial myotomes grow backwards, and become cut offfrom the remainder of the myofcomes, forming coraco-branchiales (Text-figs. 8,10). The (now) ventral ends of themyotomes grow downwards outside the Anlagen of thecoraco-branchiales forming the ventral ends of the constrictor(Text-fig. 13). The upper ends of the myotomes, in embryosbetween the lengths of 17 and 20 mm., increase in antero-posterior extent (Text-fig. 14), and, fusing together, extendbackward as the trapezius1 to the shoulder-girdle. Below

1 It is stated by van Wijhe that the seventh, eighth and ninthmyotomes give rise to " Vom Schfidel zum Schultergurtel ziehendeMuskeln nebst dem vordevsten Theile des sterno-hyoideus," but thetrapezins is not specifically mentioned by him.

MORPHOLOGY Oli' CliAN'lAL JUJSCLKS IN SO.UK VERTEBBATES. 2 3 5

the Anlagen of the trapezius each branchial myotome formsa transversely broad plate in the branchial septum (Text-fig.9). The part internal to the branchial bar forms the adductor(Text-fig. 15) ; the part external to the bar forms—next thebar, dorsally the arcualis dorsalis1 (Text-fig. 14), and belowthat the interbranchial, whilst the external edge forms theconstrictor superficialis.

In Acipenser the lower ends of the branchial myotomes

TEXT-FIG. 59.

5 0 .Buna, larva 12 mm., transverse section.

separate from the cephalic ccelom, and in 8£ mm. embryos(Text-fig. 22) grow downwards, except in the fourth brauchialsegment,2 forming the Anlagen of the coraco-branchiales,and also downwards and inwards dorsal to the cephalic coelom,forming the lower parts of the obliqui ventrales. The ventralend of the lower part of obliquus ventralis I becomes attached

1 Employing Fiirbringer's terminology (vide p. 266).5 In the adult forms examined by "Vetter the coraco-branchialis

IV was absent, and it was not developed in the embryos examined.According to Fiirbringer it is present.


to the ceratohyal, and those of the obliqui ventrales II andIII to the corresponding hypobranchials, whilst the IVth andVth meet their fellows in the median line, in the case of theIVth also becoming attached to the basibranchial. Theparts of the first three branchial myotomes above theAnlageti of the coraco-branchiales form adductors internalto the branchial bars, and the upper portions of the obliquiventrales external to the branchial bars; in the case of- thefourth myotome only the upper portion of obliquus ventralis

TEXT-FIG. 60.

6O.

Rana, larva with hind legs moderately developed, transversesection.

IV. The uppermost portions of the first four branchial myo-tomes form levatores arcuum branchialium; in 8j mm.embryos the first is attached to the auditory capsule, thesecond, third, and fourth lie outside the trunk myotomes(Text-fig. 22); in 11 mm. embryos the upper ends of the thirdand fourth have also shifted to the auditory capsule with addi-tional attachments to the second pharyngo-branchifi], and theupper end of the second has become attached to the secondpharyngo-branchial ; all four are inserted to the correspond-ing epibranchials. The trapezius is given off from the fourth

MORPHOLOGY 01' CitANIAL MUSCLES IN SOJIE VERTEBRATES. 237

levatov in 8£ ram. embryos (Text-fig. 22), and grows back tothe shoulder-girdle; in 11 mm. embryos its fore part has dis-appeared, and the anterior end of the part remaining isattached to the skin ; in the adult it is absent (Vetter). Theportion of the fifth branchial myotome above the coraco-bran-chialis V forms a muscle attached above the fourth epi-branchial and below to the fifth cerato-branchial—the fifthlevator of Vetter.

In Amia the lower end of the fifth branchial myotome formsin 8£ mm. embryos (Text-figs. 31, 32) the lateral half of atransversus ventralis V and a coraco-branchialis V, as inAcipenser; the lower end of the fourth branchial myotomeforms (Text-fig. 30) the lateral half of a transversus ventralisIV and the Aulage of the infcemrcualis ventralis IV, whichgrows forward to the third branchial bar. Neither coraco-br.m-chiales1 nor interarcuales ventrales are formed in the firstthree myotomes; the lower ends of the myotomes growdownwards and inwards, forming the ventral portions of theobliqui ventrales I, I I , and III . The portion of the fourthmyotome, next above the Anhigen of the interarcualis ven-tral is IV and transversus ventralis IV, forms the obliquusventralis of that arch, which is serially homologous with thedorsal portions oE the obliqni ventrales of the first threearches. In 15 mm. embryos the hind end of the interarcualisventralis IV grows backward to the fifth bur, and in19 mm. embryos its front portion divides longitudinally intotwo (Allis), so that there are formed two longitudinal musclesextending from the third bar to the fourth and fifth respec-tively; both are innervated by the nerve to the fourth arch(Allis).

Allis homologised these longitudinal muscles with thelower portions of the obliqui ventrales of the first threearches, but their development shows that the latter are homo-

1 Fiirbringev described a coraco-brancliialis II, but it is not des-cribed by Allis or McMurrich, and was not present in the embryosexamined.

238 V. H. EDGBWORTH.

logous with the transversi ventrales of the fourth and fiftharches.

The coi'aco-brauchialis V divides, in 14 mm. embryos, intopharyngo-clavicularis intemus and externus.

The upper ends of the first branchial myotornes form leva-tores arcuum branchialium ; the first two broaden transversely(Text-fig. 29) and divide into external and internal portions.The first and second externi and third and fourth levatores

TEXT-FIG. 61.

61 .Rana, larva with large hind legs, transverse section, c,

become attached to the first, second, third, and fourth epibran-chials, the first intemus to the second pharyngo-branchial, andsecond in tern as 1 to the third pharyngo-branchial constituentof the superior pharyngeal bone3 of Allis (os pharyngeumsuperior of v. Wijhe, Pharyngealplatte of Wiedersheim).All take their origin from the auditory capsule. The

1 Protractor laryngis of Wiedei'sheim.2 The os pharyngeum superior of Amia and Lepidosteus (Text-fig.

25) is formed by the union of the pharyiigo-branchials of the third andfourth arches—bearing out the theory of v. Wijhe.

MORPHOLOGY Ob' CBANIALMUSCLES IN SOME VKia'J'lU RATIOS. 239

trapezius is formed from the fourth levator, and persists;it is the muscle described by Allis as the " fifth externus"levator, " fouud iu 40 mm. fishes as a part of the fourthlevator." The portion of the fifth branchial myotome abovethe coraco-branchialis V does not divide into levator and(dorsal portion of) obliquus ventralis ; it forms two muscles—the second obliquus dorsalis and second adductor of Allis,passing from the fourth epi- and cerato-branchial to the fifthcerato-branchi al.

The development of the branchial muscles of Lepidosteusis similar to that of Amia, the only exceptions being (1) thecoraco-branchialis V does not divide into pharyngo-clavi-cularis externus and interims (Text-fig. 25) l ; (2) the inter-arcualis ventralis IV is not developed.

The differences between the branchial muscles of Saluioand Amia are that in the former (1) the iuterarcnalis ven-tralis IV retains the primitive condition of a longitudinalmuscle between the fourth and third bars, and does not, asin Amia, secondarily extend back to the fifth bar. (2) Thethird levator arcuutn branchialium, as well as the first two,divides into external and internal portions, of. which theexternus is inserted into the third epibranchial, and theinternns into the fourth pharyngo-brnucliial. (3) The portionof the fifth myotome above the coraeo-branchialis V formsone muscle only (obliquus dorsalis of Vetter), passing fromthe foui'th epibranchial to the fifth cerato-bvanchial. (4) Noadductor is formed in the fourth arch.

It is noteworthy that the trapezius persists in Salmo, as inMenidia (Herrick) ; in Ksox, Cyprinus, and Perca it is absentin the adult (Vetter). Iu some Teleostei there are a greaternumber of interarcuales ventrales present than in Salmo,e . g . in Cyprinus an interarcualis ventralis I, and iu Esoxan interarcualis ventralis I I I are additionally present (Vetter).

The muscles attached to the ventral ends of the branchialbars o£ Polypterus, apparently, are very different in various

1 According to Furbringer, " Lepidosteus hat kehi coraco-branchialismehr."

240 K H. EDGKWOIiTH.

species. Fiirbringer stated that in Polypterus, ? species, thereare four coraco-branchiales attached to the four branchial bars.Pollard did not describe these; lie stated that in Polypterus,? species, the coraco-hyoideus sends additionally a longtendon to the lower end of the first cerato-branchial, and alsothat there is a muscle belonging1 to the system of the coraco-arcuales, which, arising from the fourth, i . e . last cerato-branchial, passes horizontally forwards and affixes itself tothe lower euds of the second and first cerato-branchiales. Itis apparently supplied by the united first and second spinal

TEXT-FIG. 62.

62.RLUUI. larva with fully formed hind legs, transverse section.

nerves. There is also " a fiat muscle of small size, whichtakes its origin from the lust cerato-branchial. It losesitself in the skin near the anterior edge of the dermal clavicle.Its innervafcion was not traced."

In P o l y p t e r u s Senegal us (larvae 7£ to 9.| cm. long)there is a pha.ryngo-clavicularis externus and interims ( =coraco-branchialis IV) attached anteriorly to the fourthcerato-branchial, and passing downwards through the coraco-hyoideus to the shoulder-girdle (Text-fig. 37). In front ofthis is a longitudinal muscle passing from the fourth to thesecond cerato-branchial, and innervated by the nerve to the

MOKPHOLOUY OF CRANIAL MUSCLES IN SOME VKKTEBUATES. 241

third arch; this, on comparison with the interarcualis ventralisIV of Amia, is probably an interarcualis venbralis I I I , whichhas additionally extended back to the fourth bar. In frontot this are the interarcuales ventrales I I and I, the formerpassing from the second to the first cerato-branchial, and thelatter from the cerato-branchial to tlie ceratohyal (Text-figs.35 and 36).

In P o l y p t e r n s s e n e g a l u s there are transversi ventrnlesIII and IV (Text-figs. 36, 37); the median edges of theformer are attached to the basibranchial; the latter in itsanterior part forms a transverse muscle, and in its posteriorpart enters into relation witli the rima glottidis, forming thedilatator of Wiederslieim. He called the fore part of themuscle M. adductor arc. branch., but adductors, in the senseof Vetter, are not present in P o l y p t e r u s s e n e g a l u s , andthe whole muscle is a transversus ventralis of the fourth arch.

lu Polypterus, ? species, Pollard described four "iuter-arcuales veutrales " ( i .e . in the terminology of this paper," obliqui ventrales"), one to each branchial bar. In Po ly -p t e r u s senega lus these muscles are not present in the firstand second branchial segments; in the third and fourthsegments their dorsal portions are present in the form of veryminute muscles, the lower ends oE which are attached to thecerato-branchiales (Text-fig. 37). Pollard described four leva-tores arcuum branchialium inserted into the upper ends of thecerato-branchials. In P o l y p t e r u s s e n e g a l u s the first isinserted into the first pharyngo- and epi-branchial, the secondand third into the respective pharyngo-branchials, and thefourth, which has an additional head from the third pliaryngo-branchial, into the fourth cerato-braucliial. According toPollard, there is no trapezius corresponding to that ofSelachians, but he mentions that a muscular slip—presumablyof the fourth levator—continues on beyond the last (fourth)cerato-branchial, and is inserted into the skin-ligaments infront of. the shoulder-girdle. In P o l y p t e r u s s enega lusthere is a trapezius arising in common with the fourthlevator and passing back to the shoulder-girdle (Text-tig. 37).

242 F . H . KDGKVVOKTH.

The development of the branchial muscles of Ceratodus, asgiven by Greil, is summarised above (pp. 175 and 176). In thespecimens examined the lower ends of tlie branchial myotomesseparate from the lateral wall of the cephalic coelom in stage42 (Text-figs. 42, 43). In stage 46 the lower end of the firstbranchial myotome grows forward to the hypohyal (Text-fig.44), forming the interarcualis ventralis P s. branchio-hyoideus;

TEXT-FIG. 63.

63.Alyfces, larva 12 mm., transverse section.

in the second, third, and fifth branchial segments the lower endsof the myotomes grow downwards, forming coraco-branchialesII (Text-fig. 47), III and V, and also downwards and inwards,forming the (lateral halves of the) transversi ventrales

1 Cerato-liyoideus interims of Fiir bringer ; cerato-hyoidens of Gveil;M. f^rand abducteur dn premier arc branchial of Jaquet, who statesthat the hind end of the muscle is attached to the first and secondbranchial bars.

MORPHOLOGY OT? CRANIAL MUSCLES IN SOMF, VERTEBRATES. 243

II,1 III ,1 and V - ; in the foui'th branchial segment only acoraco-branchialis IV is formed. This condition—of aninteravcualis ventralis I and coraco-brancliiales I I , I I I , IV,and V—persists till stage 6 3 ; at a later stage the hinder endof the interarcualis veutralis I grows backwards, forming,in the specimen examined, a longitudinal muscle, which isattached posteriorly to the fifth bar, and also a coraco-bran-chialis I. From this and the descriptions given of the adultby M. Fiirbringer and by Jaquet, it may be inferred thattlie hind end of the interarcualis ventralis I always growsback, forming a coraco-branchialis I, and may or may notalso grow back to a more posterior branchial bar.

The portions of the branchial myobomes immediately abovethe interarcualis ventralis I and coraco-branchiales I I , I I I ,and IV form Mm. marginales.3 No adductors are developed.The upper ends of the first four branchial myotomes and thewhole of the fifth branchial myotome above the coraco-bran-chialis V (no fifth M. marginalis being developed) formlevatores arcnum branchialium4 (Text-fig. 48).

The trapezius5 is proliferated from the outer side of the fifthlevator in stage 48 (Text-fig. 48).

In Necturus (Miss Platt), in embryos of 12-J- mm. there isan outgrowth from the ventral part of the glosso-pharyngealmuscle—the beginning of the cerato-hyoideus internus; andthere are three constrictors arcuura, the first growing forwardsfrom the mesothelium of the first vagus arch where this joins

1 M. cluasmique of Jaquet; second and. third Mm. intei'branchialesof G-reil.

2 The posterior margin of the transversus ventralis V in stage 63underlies the lung.

3 M. branchialis of Jaquet; first, second, third, and fourth Mm.interbvanchiales of K. Furbringer; fourth and fiftli Mm. interbranchialesof Greil. In the adult, according to Jaquet, these muscles are attacheddorsally to the upper ends of the branchial bars, according to K.Fiirbringer to the skull.

4 Cranio-branchiales of Jaqnet; levatores arcnum branchialium ofGreil.

5 M. scapulo-branchialis of Jaquet; levator scapula; of Greil.

244 ]?. H. EDGEWOJtTH.

the wall of the pericardium, the second and third arising as asingle muscle from the wall of the pericardium in the regionwhere the mesothelium of the second vagus arch unites withthe pericardial wall. Above these muscles are found the gill-muscles, and dorsally the three levatores arcuum.

This would mean, according to the theory which wassuggested above, that the interarcuales ventrales I, II, andI I I are formed from the ventral ends of the first, second,and third branchial myotomes, the Anlagen of the gill-muscles above these, and the three levatores from the upper-most portions.

There are three other branchial muscles in Necturus whichwere not mentioned by Miss Platt—the transversus ven-tralis IV,1 fourth2 levator arcuum, and the trapezins.2 In 12mm. embryos there is present a fourth branchial myotomeserially homologous with the first, second, and third (Text-figs.51, 52). In 13 mm. embryos this has sepnrated from thecephalic coelom and divided into a fourth levator and lateralhalf of a transversus ventralis IV (Text-fig. 53); in 14A mm.embryos the lower half of the transversus ventralis IV hasspread inwards dorsal to the cephalic coelom and below thedeveloping larynx to meet its fellow in the middle line (Text-fig. 56).3 ISTo interarcualis ventralis IV is developed. Trans-versi ventrales are not developed in the first three arches.3

The trapezius is proliferated from the outer surface of thefourth levator in 16 mm. embryos.

In Tr i ton c r i s t a t u s the events are similar; an interarcu-alis ventralis IV is developed, in correlation with the formationof the fourth branchial bar. The interarcuales ventrales II,III , and IV become divided into the muscles called sub-

1 The fourth pharyiigo-branchialis of Wilder: the hyo-phavyngeus ofG-oppert.

2 The foirrth levator and trapezius were described by Mivart; thelatter, in the terminology of Fiirbringer, is a dorso-scapularis.

3 This confirms the opinion of Gopperb that his hyopharyngeus isnot formed by fusion of transversi ventrales III and IV, but is only atransversus ventralis IV.

MOHPHOLOGY OF CRANIAL MUSCr,KS IN SOMIO VERTEBRATES. 245

arcuales recti and obliqui by Driiner. The trapezins is acapiti-dorso-scapularis; it is formed by proliferation from theouter surface of the fourth ]evator in 8 i mm. (just hatched)larvae.

Driiner described in Urodela a first, third, fourth, and fifthtransversus ventralis (called by him "interbranchial") in tlieterritory of the first, third, fourth, and (an atrophied) fifthbranchial arches. He also stated that the first is formed bya secondary attachment of the ventral facial muscles to thefirst branchial arch—this, which is not a true transversns, isdescribed above (p.215). In Necturns and T r i t o n c r i s t a t u sa transversus ventralis I I I is not formed; tliere is only alVtli. The question whether the laryngei represent a Vthis discussed below. The transversi veutrales were includedby Driiner in the ventral head muscles, but they are notserially homologous with the intermandibularis and inter-hyoideus, which are developed from the walls of the cephalicccelom in the mandibular and hyoid segments, whereas thetransversi ventrales are formed by downgrowths of thebranchial myotomes dorsal to the cephalic coolom.

In I t a n a t e m p o r a r i a the ventral ends of the fonrbranchial rayototnes separate from the parts above in 6A mm.embryos, and form the Anlagen of the fonr interarcualesventrales, and in the second, third, and fourth segments theAnla.gen of the trausversi venti-ales. Iu the first three seg-ments the middle portions of the myotomes form the Mm.rnarginales and the upper parts the levators. The portionof the fourth myotome above the interarcualis ventralis formsthe fourth levator, no M. marginalis being developed.

The median ends of transversi veutrales I I and I I I becomeattached to the posterior surface of a ventral projection ofthe first basibrauchial (second copula), and their lateraledges to the processus branchialis. The lateral edges oftransversus ventralis IV become attached to the fourth cerato-branchial (Text-fig. 61), and their median edges meet in acentral raphe, which underlies the fore part of the larynx.There are similar muscles in larvaa of Alytes, Bufo l e n t i -

246 1\ H. JiDGEWORTH.

g inosus , and Pelobates.1 In Rana, at the end of the rneta-morphosis, the transversi ventrales II and I I I disappear,whilst transversns ventral is IV persists.

Wilder was of opinion that transversus ventralis IV(constrictor laryngis, hyopharyngeus of Goppert, Veren-gerer des Aditus laryngis of Henle) was a derivative of theintrinsic ring, i . e . of the sphincter laryngis. Goppert, onthe other hand, thought that it was homologous with thehyopharyngens of Urodela, only differing in that it failsin the larva to be attached to the fourth bar. Thishomologyof Goppert is confirmed by the development of the muscles.In the Anurau larvse examined the muscle was attached tothe fourth bar.

The Anlagen of the interarcuales ventrales develop intolongitudinal muscles, each extending from the ba.r of itssegment of origin to the next anterior one. In 9 mm. larvaathe interarcualis ventralis I s. branchio-hyoideus divideslongitudinally into two parts, one of which connects the firstbranchial bar to the ceratohyal, the other forms with theinterarcualis ventralis I I a muscle extending from the secondbranchial bar to the ceratohyal. A similar development ofthe interarcualis ventralis I takes place in Bnfo l e n t i -g inosus , Alytes, and Pelobates.3

The Mm. marginales of Alytes, Bufo, Ra.na, and Pelobates(vide Schultze), run along the external edges of the corres-ponding branchial bars ; their dorsal ends are attached to theexternal surfaces of the upper ends (below the insertions of thelevators) of their respective bars. The ventral end of the firstis attached to the second bar—to the processus branchialis ofSchultze, which is formed from the second bar, the ventral

1 The transversi ventrales II and III are collectively termed " basi-hyobranchialis " by Schultze, in Pelobates.

3 Schultze did not describe the muscle passing from the firstbranchial bar to the ceratohyal in older larvae of Pelobates, but it per-sists up to the stage of 30 mm. The interarcuales II and III hecollectively terms the " interbranchial" ; and the muscle passing fromthe second bar to the ceratohyal the " cerato-hyo-branchialis."


ends of the second and third to the third bar, just behindits junction with the processus branchialis. In Rana, at tlieend of metamorphosis, the cerato-branchial portions of thebranchial bars disappear and the Mm. marginales also. Theupper eud of the first levator becomes attached in part tothe palato-pterygoid bar and in part to the periotic capsule,the second, third., and fourth to the periotic capsule only(Text-fig. 61). This is also the case in Alytes, Bufo l e n t i -g i n o s n s , and Pelobates.1

According to Wilder, in R a n a c l a i n i t a n s the fourthlevator is formed during metamorphosis by division of thedorso-lavyngis into the fourth levator, and dilatator laryngis ;and this is stated to hold generally in Anura. In R a n at e m p o r a r i a , however, the fourth levator is formed in 7 ram.embryos, and the dorso-laryngeus not until 7 | mm., and thetwo muscles have no genetic connection ; aud both musclesare present in larvae of Pelobates, Alytes, and Bufo l e n t i -g i n os u s, of 10, 12 J, and 10 mm. respectively, i . e . long beforemetamorphosis.

In Rana, late in metamorphosis, the partial origin of thefirst levator from the palato-pterygoid bar is given up, and,on the atrophy of the cerato-branchial s and Mm. marginales,all four levators extend downwards, and their lower endsbecome attached to the body and processus posterior mediusof the hyoid bar.

In 12 mm. larvae of Rana a downgrowth of the lower endof the fourth levator takes place, forming the diaphragrnato-branchialis lateralis2 (of Schultze). Its upper end becomesattached to the fourth bar, its lower end to the diaphragm.I t is innervated by the Xth. I t is also formed in Alytes,

1 Sclraltze, in older lai-vse of Pelobates, described all four levatores asarising from the palato-quadrate bar.

2 Schultze gave tlie name "diaphragniato-branchialis medialis " tothe muscle called " sterno-hyoid " in this paper. He did not describethe innewation or development of the larval muscles of Pelobates ; hisnames are purely descriptive, and do not imply that he thought that thetwo muscles " diaphragmato-branchialis" and "medialis" have anygenetic connection.

VOL. 56, PART 2. NEW SERIES. .1.8

248 F. H. EDGUWORTH.

Bufo l e n t i g i n o s u s , and Pelobates, in larvaa of about thesame length. In Rana it disappears late in metamorphosis.The trapezius (capiti-scapularis, of Fiirbringer; cucullaris,of Eckerand Ganpp) is formed eai-ly in metamorphosis fromcells proliferated from the outer surface of the fourth levator(Text-fig. 61).

In 6 mm. embryos of Chrysemys m a r g i n a t a there arefour branchial myotomes; in 8 mm. embryos (Text-figs. 66-69)the middle portion of: the first is very slender and that of thesecond has disappeared, and the middle and lower portionsof the third and fourth have disappeared ; the upper end ofthe fourth has extended back a little in the neck, the upperend of the third has extended back to that of the fourth, theupper end of the second is a sepai-ate structure, and the upperend of the first is still connected with the rest of the myotome.In 12 mm. embryos the dorsal ends of the first and secoudhave each grown backwards into the next segment, and thereis thus formed a loug column of cells which has grown stillfurther backwards into the neck, forming a trapezius—thecapiti-plastralis of Furbringer; the middle portion of thefirst and the lower end of the second myotomes1 have dis-appeared, whilst the lower end of the first forms the inter-arcualis veutralis I, which, extending from the first branchialbar to Meckel's cartilage, is the branchio-mandibularis.

In L a c e r t a ag i l i s the dorsal edge of the primitivetrapezius extends upwards outside the trunk inyotomes of theneck (Text-figs. 70, 71), and in 20 mm. embryos it has dividedinto dorsal and ventral portions, the capiti-dorso-clavicularisand capiti-cleido-episternalis of Furbringer. The former isinnervated solely by spinal nerves, the latter by the acces-sorius vagi. Fiirbringer concluded from this innervationthat the capiti-dorso-clavicularis is a new formation, aud that

1 The curious persistence for a time of the lower end of the secondbranchial myotome, after disappearance of the middle portion of themyotome, is in favour of the idea (loc. cit.) that ancestors of theSauvopsida may have possessed an interarcualis ventralis II, passingfrom the second to the first branchial bar.


the whole muscle is a complex of muscle-metameres,1 but thisinference is not borne out by study o£ its development.

In Gallus the upper ends of the first and second branchialmyotomes separate from the parts beneath on the fourth day(Text-figs. 72, 73). They fuse together and extend back-wards in the neck (Text-fig. 74) forming the trapezius

TEXT-FIG. 64.

6 4 .Text-figs. 64-69.—Chrysemys. embryo S mm. Text-fig. 64 is the

most anterior; Text-figs. 64 and 65 are through the hyoidsegment, Text-fig. 66 through the first branchial. Text-fig. 67through the second branchial. Text-fig. 68 through the thirdbranchial, and Text-fig. 69 through the fourth branchial seg-ment.

(Cucullaris of Fiirbringer). The lower end of the firstbranchial myotome forms the interarcualis ventralis I s.

1 " So entstand em nengebildeter, dem ursprunglichen M. cucullarisnur in seinen voidersten Theile homologer, in seinen Hauptmasse aberbios initatorisch-hoinodynamer odev parhomologei' Muskel."


branchio-mandibularis. The middle portion of the first andthe whole of the second (below the Anlage of the trapezius)branchial myotomes disappear.

In 5 mm. embryos of the rabbit the upper ends of the first,second, and third branchial myotomes separate from the partsbelow, the upper end of the third grows backward in theneck, and the upper end of the second backward to join that

TEXT-FIG. 65.

tVJOCtt- wOI^ .

6 5.

of the third (Text-figs. 85, 86, 87); in 6 mm. embryos theupper end of the first has grown back to that of the second.The hind end of the pi-imitive trapezius, thus formed from theupper ends of all three bi*anchial myotomes, reaches theanterior limb area in 7 mm. embryos (Text-fig. 88); its dorsaledge extends upwards in 7A mm. embryos (Text-fig. 90), andin 9 mm. embryos it has divided into the trapezius and

MOKPHOLOGY OF OKANLV1, MUSCLES IN SO.ME VERTEBRATES. 251

TEXT-PIG. 66.

67.

252 1<\ i t . EDGEWOKTK.

TEXT-FIG. t>8.

6 9 .


sterno-mastoid of the adult. The portions of the branchialmyotomes below the Anlagen of the trapezius have dis-appeared in 7 mm. embryos.

In the pig the lower end of the first branchial myotornepersists (Text-fig. 98), and forms the interarcualis Ventralis Is. branchio-hyoideus (Text-fig. 99). This muscle is also con-stantly present in the dog/ and in Mouotremes,3 and is occa-sionally present in man.* In Monotremes there is also aninterarcualis ventralis I I I passing from the third to thesecond, branchial arch.1

O N THE H O M O L O W I K S BKTWJBBN THE BRANCHIAL MUSCLES Ob'

ArAKious VERTEBRATES.

(1) The H y p o b r a n c h i a l Cran ia l Muscles.—Thelower ends of the branchial myotomes develop into longi-tudinal muscles—interarcuales ventrales, and coraco bran-chiales—in Selachii, Teleostomi, Dipnoi, Amphibia, andMammalia. Their innervatiou varies. Those which remainin their segment of origin, or nearly so, extending forwardto the ventral end of the next anterior branchial bar orhyoid bar (or additionally and subsequently to the next pos-terior bar, in Amia, and probably P o l y p t e r u s senegalus)are innervated by the corresponding branchial nerve, IXth orbranch of Xch, or by this and the next anterior branch.This holds for the interarcuales ventrales of Amia,P o l y p t e r u s s enega lu s , Salmo, Ceratodus, Amphibia, andMammalia. The interarcualis ventralis I of Sauropsida(brancliio-hyoideus or branchio-mandibularis) is an exceptionto the rale; it is innervated by the Xllth.

A coraco-branchialis, or pharyngo-clavicularis extern us andintern us, developed bybackward growth from thelast branchialmyotome, i . e . fourth in P o l y p t e r u s senega lus , fifth

1 Keiato-hyoideus of EUenberger and Baiini.2 Interhyoideus of Dubois.3 Kemto-tliyi'o-hyoideus of Shattuck.4 Intertliyroideus of Dubois.

254 • F. R. EDGEWORTH.

in Amia, Salmo, Esox, Menidia, may either retain its originalbranchial innervation from tlie Xth, e. g. Amia (Allis),Bsox (Vetter), Menidia (Herrick), Lepidosteus, P o l y p t e r u ssenega lus , or be innervated by spino-occipital nerves, e. g.Amieurus (Wright), Salmo (Harrison). When coraco-branchiales are developed from all tlie branchial myotoines,they are innervated by the spino-occipital nerves, e. g.Selachvi (Vetter, Fiirbringer), Acipenser (Vetter), Polypterus? species (Fiirbriuger), Ceratodus (Fiirbringer).

The coraco-branchiales muscles have been generally classedwith the hypobranchial spinal muscles, but investigation ofdevelopmental stages shows that the ventral ends ofbranchial myotomes maj' form longitudinal muscles, whicheither grow forwards, forming interarcuales ventrales, orbackwards, forming coraco-branchiales, but not in bothdirections. (There are two, probably three, exceptions tothe above rule; in Amia, at a late stage of development, thehind end of the interarcualis ventralis IV grows backwardto the fifth bar; the innervation in P o l y p t e r u s sene-ga lus suggests that the hind end of the interarcualis ven-tralis I I I similarly grows back to the fourth bar; and inCeratodus the hind end of the interarcualis veutralis I, at alate stage of development, grows back, forming the coraco-branchialis I, and also, at least in some cases, to a moreposterior bar.) The first condition, that of interarcualesventrales, is the primary one, as shown by the correspondenceof cranial nerve innervation, with segment of origin. Thesecond condition, that of coraco-branchiales, is a secondaryone, in which a change of function to one very similar tothat of the coraco-hyoideus is correlated, though iu varyingdegree, with a change of inuervation to one by the spino-occipital nerves.

An approximation to what was, probably, the primitivecondition, is seen in Amphibia. This was a series ofinterarcuales ventrales, each extending from the bar of itssegment of origin to the next anterior one. The hyo-maxillaris, in the hyoid segment, is serially homologous with


the branchial interarcuales ventralos. There is no hoinologuein the mandibular segment. These longitudinal musclespossibly date from a period where tliere were no mediancartilages connecting the ventral ends of the hyoid andbranchial bars, and formed a recfcus system of the headserially homologous with that of the body, though nowcovered over by the latter, owing to its extension forwardsinto the head.

TEXT-FIG. 70.

7 0 .

Lacerta, emlvryo S mm., transverse section. The light side ofthe section is a little anterior to the left.

(1) Transversi Ventrales, Mm. Margiuales, andObliqui Ventrales.—in Scyllium, Acanthias, Sauropsidn,rabbit, and pig, the hypobranchial cranial muscles are the mostventral ones formed from the branchial myotomes; no trans-versi ventrales are formed. This is also the case in the firstbranchial segment of Anurau tadpoles, the first, second, andthird of the Necturus and Triton, the first and fourth ofCeratodus, the first and second of Polypterus senega!us.

256 1'. H. EDGEWOfiTH.

But in the second, third, and fourth branchial segmentsof Anuran tadpoles, the fourth of Necturus and Triton, thesecond, third, and fifth of Ceratodus, and in those segmentsof Teleostomi in which hypobrauchial cranial muscles areformed, the lower ends of the branchial myotomes also growdownwards and inwards above the cephalic ccelotn, towards,or to the middle line forming the (lateral halves of the)transversi ventrales, or their homologues, the lower portionsof the obliqui ventrales. In branchial segments of Teleostomi,where hypobranchial cranial muscles are not formed, i . e .first four of Lepidosteus, first three of Amia and Sal mo,fourth of Acipenser, there is a similar downward and inwardgrowth of the ventral ends of the branchial myotomes, toform the lower portions of the obliqui ventrales.

The hinder part of the transversus ventralis IV of Polyp-terus and Amphibia, and of the transversus ventralis Vof Ceratodus, comes into intimate relations with the ventrallarynx, though in varying ways, underlying it in Amphibiaand Ceratodus, forming a dilatator in Polypterus.

The portions of the branchial myotomes next above theAnlagen of the hypobranchial cranial muscles form theAnlagen of the muscles of the external gills in the firstthree segments of Necturus and Triton, and the Mm. mar-ginales in the first three segments of Anuran larvse aud thefirst four segments of Ceratodus. Homologous Anlagen formthe upper portions of the obliqni ventrales in Teleostomanembryos—of the first four segmeuts of Acipenser, Lepi-dosteus, Amia, Salmo, Polypterus (Pollard), and of the thirdand fourth segments of P o l y p t e r u s senega lus ; these mayor may not unite with the lower portions. In some-segmentsof Teleostomi, i. e. first three of Acipenser, fourth of Lepi-dosteus, Amia, and Salmo, adductors are formed from por-tions of the myotomes lying internal to the branchial bars;they are not developed in Polypterus.

In Scyliium the portions of the branchial myotomes nextabove the Anlagen of the coraco-branchiales form adductorsinternal to the branchial bars, and the superficial con-

MOllPHOLOUY OF CRANIAL MUSCLES IN SOATti V.EKTH.BKATKS. 257

strictors, interbranchials, aud arcuales dorsales external tothem. The lower ends of the superficial constrictors extenddownwards external to the coraco-branchiales, but such down-growths do not appear to be homologous with the traus-versi ventrales or inferior portions of the obliqui veutralesof Teleostomi, Ceratodus, and Amphibia.

In Sauropsida, rabbit, and pig embryos the portions ofthe branchial myotomes next above the Anlagen of the hypo-brauchial cranial muscles, aud also the lower ends where theseAnlagen are not formed, atrophy.

Levatores arcunm branchialum are developed from theupper ends of the branchial myotomes in Teleostomi, Cera-todus, and Amphibia, but are not developed in Scyllium,Sauropsida, rabbit, and pig. The method of development ofthe trapezius—apparently a homologous muscle throughoutthese vertebrate groups—is intimately related to these differ-ences. I t is developed in Teleostomi and Amphibia from thefourth, in Ceratodus from the fifth, levator, i. e. from thepenultimate or ultimate levator1; whereas in Scyllium,Chrysemys, Gall us, and rabbit, it is formed from the upperends of the branchial myotomes—five in Scyllium, four inChrysemys, two in Gallus, and three in the rabbiD.

In view of the facts that in Scyllium the subspinalis andinterbasales, developed from trunk-myotomes, are attachedto the pharyngo-branchials, and that the trapezius is inner-vated only by the Xlth—the most posterior of the vagusroots—even though a constituent from the glossophavyngeal(first branchial) segment takes part in its formatiou, it isprobable that the absence of levatores aud associated methodo£ development of the trapezius in Scyllium, Sauropsida, andrabbit are secondary phenomena, and that the primary con-dition is a series of levatores formed from the uppermostportions of the branchial myotomes. This theory would alsoafford an explanation of the curious fact that whereas the

' In Teleostomaii embryos the trapezius is developed from the upperedge of the levator, in Ceratodus and Amphibia from its externalsurface.

258 i\ H. EDGBWORTH.

general development of the rayotomes takes place from betorebackwards, the separation of the upper ends of the branchialmyotomes, their backward growth, and fusion to form atrapezius, in Scyllium, Clirysetnys, Grallus, and Lepus, takeplace from behind forwards—the process beginning in thelast branchial myotome.

Adductors of the branchial bars are formed in Scylliuuiand in certain segments of some Teleostomi, on the inner

TEXT-FIG. 71.

7 1 .

Lacevfca, embryo 12 mm., transverse section.

side of the branchial bars. The observations oE Balfour1

showed that the primary situation of the muscles is oneexternal to the bars, so that the non-development of adduc-tors in Amphibia, Ceratodus, and Polypterus would appear torepresent a primitive condition.

It may be added that the adductors of the branchial barsare not serially homologous with the adductor mandibulfe.which is formed external to the mandibular arch.

1 ' Comparative Euibvyology,' vol. ii, p. 471.

MOEPHOJ-OOY Of CRANIAL JMUSCLES LJST SOME VERTEBRATES. 259

The simplest and probably primary condition of themuscles developed between the levatores above and thehypobi'anchial cranial mnscles below is a series of Mm.marginales, as found in Anuran larvae and Ceratodns. InTeloostomi these may unite with the (lateral halves of the)transversi ventrales. In Scyllium they undergo a quitespecial development, which is not found in any other group.

The above comparisons suggest that the probable primitivecondition of each of the branchial myotomes was, fromabove downwards, a levator, a M. marginales, an inter-arcnalis ventrales, and (the lateral half of a) transversusventralis.

CEsophf i^ea l , Ph ai'y n g-ea 1, a n d L a r y n g e a l M u s c l e s .—The term " p h a r y n x " is employed by writers in two senses,either restricted in meaning' to the branchial region of thealimentary canal, or including this and the next succeeding

. portion. In this paper it is used in the first sense.The oesophagus is surrounded by a circular muscle, the

constrictor, which is derived from cells given off from thesplanchnic layer of the coelomic epithelium.

No circular muscles are present in the branchial region ofSelachii, Acipenser, and Ceratodus, but are present, in theform of transversi dorsales, in Teleostomi (Vetter), Arnia(Allis), aud Lepidosteus (Wiedersheim), and are formed bythe constrictor of the oesophagus extending forwards,dorsally, into the branchial region. In P o l y p t e r u ss e n e g a l u s the fore part of the oesophageal constrictorslightly overlaps the branchial region dorsally, but thetransversely directed fibres are not attached to any branchialbar. In Lepidosteus and Amia1 the conditions are coin-plicated by the presence of a dorsal larynx. The dorsallarynx of Lepidosteus is formed, in 8 mm. embryos, as asolid median upgrowth from the then solid oesophagus justbehind the branchial region. The oesophageal constrictor(constrictor pharyngis of Wiedersheim) is formed from cells

1 The adult condition of the dorsal larynx and its musculature hasbeen fully described by Wiedersheim.

260 V. H. EDGEWORTH.

given off from the coelomic epithelium ; it spreads upwardsround the cesophagus and dorsal larynx, forming the con-strictor lai-yngis, and subsequently, in 9. mm. embryos,spreads forward to the branchial region and becomes attachedto the os pharyngeum superior (of van Wijhe, the Pharyngeal-platte of Wiederslieim) forming the transversus dorsalis andfirst obliquus dorsalis. The dilatator laryngis is formed fromthe dorsal part of the cesophageal constrictor (Text-fig. 32).The development of the retractor and protractor laryngis isdescribed on pp. 238 and 267.

The development of the dorsal larynx of Amia is similar tothat of Lepidostens. The forward extension of thecesophageal constrictor begins in 8£ mm. embryos (Text-figs.30, 31, 32); it forms the transversus anterior and posteriorandnrst obliquus dorsalis (of Allis). I nSa lmo far io the trans-verse fibres become attached to the fifth cerato-branchial, thefourth pharyngo- and epi-branchial and the third pharyngo-branchial.

The ventral larynx and musculature of Polypterus havebeen described by Wiedersheim, who says, that the musclesconsist of a dilatator and sphincter glottidis, the latter of•which is continuous below with a muscle-sheet surroundingthe lungs. As stated above, the dilatator is the trans-versus ventralis IV. The sphincter glottidis is continuousabove with the constrictor of the cesophagus, which is notattached laterally to the trunk muscles.

The development of the ventral larynx of Ceratodushas been described by Kellicott, and the adult conditionby Wiedersheim. It may be added that the posterior edgeof transversus ventralis V underlies the lung, and that, thoughthere is no dorso-laryngeus (Wiedersheim), the lateral edgesof the constrictor of the oesophagus are attached to thelower ends of the trunk-myotomes (Text-fig. 49).

It was supposed by Gegenbauer, Wilder, Goppert, andDriAner, that the cartilagines laryngei of Amphibia werebranchial bars, and that the laryngeal muscles were deriva-tives of branchial muscles. Wilder stated that the dorso-


laryngei s. dorso-tracheales were serially homologous withthe levatores arcuum branchialium (called by him " dorso-branchiales " ) , that the laryngei were homologous with thetransversi ventrales (called by him " pharyngo-branchiales ") ,and that these muscles and the laryngeal cartilages belongedto the fifth branchial arch.

This theory of the nature of the laryngeal muscles wasformed on the evidence of adult anatomy only, withoutknowledge of the method of development.

Wiedersheiui stated that the fibro-cartilage present inassociation with the ventral larynx of Protopterus might bedue to the remains of a sixth arch, "noch plausibler abererscheinfc es rair die befcreffenden Knorpel aut' einen in derRaphe des phai^yngealen Constrictors sich abspielendenChondrificationsprocess, das heisst auf Muskelwirkungziiruckzufuhren"; also that " a priori stelit der Annahinegewiss nichts in der Wege das sich auch bei Avnphibien dieprimitive Cartilago lateralis als eine Sehnenvei-knorpelungbilden kann ohne das dabei phylogenetische Beziehung zuden Kievnenbogen angenominen werdea mussen."

In Necturus the larynx is formed as a median ventralpouch of the pharynx in the hinder part of the fourthbranchial segment in 13 mm. embryos (Text-figs. 53, 54). Thecells which form the constrictor of the oesophagus are buddedoff from a thickened portion of the splanchnic ccolomicepithelium, and spread upwards round it (Text-fig. 54). Asimilar production of splanchnic mesoblast from a thickenedportion of splanchnic ccelomic epithelium takes placein the fourth branchial segment (Text-fig. 52), and thecells spread upwards round the developing larynx andpharynx. In ]4£ mm. embryos this splanchnic meso-derm spreads upwards on either side of the pharynxinternal to the fourth levatores arcuum branchialium, andforms the Aulagen of the dorso-laryngei and of the pharyn-geal constrictor (Text-fig. 56). The splanchnic mesodermventral to the pharynx develops into the laryngei muscles,and, next the larynx, the laryngeal cartilages.

262 F. H. "EDGEWORTH.

A similar development of the laryngeal muscles takesplace in Triton and in Rana.

If the method of: development of the laryngeal muscles becompared with that of the branchial muscles it is seen thatthey are very different. The bi-anchial muscles are developedfrom the branchial myotornes, the laryngeal muscles aredifferentiations of an cesophageal or pharyngeal constrictor,which is formed from cells given off by the ccelomic epi-thelum. In Polypterus and Ceratodus the larynx isdeveloped just behind the branchial region, in Amphibia inthe last, i . e . fourth branchial, segment. In Polypterus thecesophageal constrictor is not attached to the trunk-myotomes; in Ceratodus it is attached, though no dorso-laryngei are developed; in Amphibia dorso-laryngei aredeveloped. In Ceratodus there are no intrinsic laryngealmuscles; in Polypterus there is a sphincter glottidis, whichremains in continuity with the constrictor of the oesophagus;in Amphibia there are laryngei or a sphincter laryngis,which is not continuous with the constrictor of the pharynx.In Polypterus and Ceratodns there are no skeletal structures ;in Amphibia laryngeal cartilages are developed—later thanthe branchial bars and ventral, not lateral to the pharynx.These similarities and differences suggest that the conditionsfound in Polypterus and Ceratodns preserve stages in thephylogenetic development of the laryngeal structures ofAmphibia. They tend to confirm the theoi-y of Wiedersheim.The relations of the transversns ventralis of the last branchialsegment (fourth in Polypterus and Amphibia, fifth in Cera-todus) to the laryngeal structures have been described above.

In 5 mm. embryos of Chrysemys the opening of the larynxis in the fourth branchial segment; the coelomic epithelurn inthe third and fourth branchial segments is thickened andproliferating mesoblast cells, which surround the pharynxand developing larynx. In 8 mm. embryos the opening ofthe larynx is in the third and fourth branchial segments; inthe fourth a constrictor pharyngis is formed from thesplanchnic mesoblast; in the third and fourth the Anlagen of

MORPHOLOGY OF CRANLVL MUSCLES IN SO^Ui VERTEBRATES. 263

the sphincter laryngis and dilatator laryngis (Text-fig. 69) areformed, the latter having a vertical position and passing upoutside the vagus. The dilatator has lost this position in15 mm. embryos, and its hind end is attached to the cricoid.This supports the theory of G-dpperb that the dilatatorlaryngis of Sauropsida is the homologue of the dorso-la.ryn-geus, and the sphincter the homologue of the sphincter andlaryngei of Amphibia.

In 3 mm. embryos of the rabbit, cells are proliferated fromthe coelomic epithelium in the three branchial segments(Text-fig. 80) ; they spread upwards internal to the branchialaortic arches. In 5 mm. embryos they have spread a littleround the pharynx in the second and third branchial segments(Text-figs. 85, 86), but in the first they exist only lateral toit. In 6 mm. embryos the splanchnic mesoblast forms a con-tinuous sheet dorsal to the pharynx in the second and thirdsegments, but in the first it is still only lateral to it. In7 mm. embryos it is present there also, more probably as aresult of forward extension from the second branchial seg-ment than of upward extension in the first segment. Thiscontinuous splanchnic mesoderm sheet is continuous behindwith that round the oesophagus (Text-fig. 90), which isformed in a similar way.

The stylo-pharyngeus is formed in the splanchnic meso-blast of the first branchial segment; it is first visible in7$ mm. embryos and gains an attachment to the hyoid bar(Text-fig. 93). The pharyngeal constrictor is also formed inthe three branchial segments, though, perhaps, v i d e s u p r a ,derived from cells of the second and third segments only.The Anlage of the laryngeal muscles is also visible in 1\ mm.embryos in the third branchial segment. The later develop-ment of the laryngeal muscles, in man, has been traced byFrazer, who says that they are developed in the third bran-chial segment from the ventral parfc of the layer of: cellsround the pharynx and larynx; of this laryngeal portion" the formation of the arytenoid seems to convert the dorsalhinder part into the crico-arytenoideus posticus, tlie upper

"VOL. 5 6 , PATCT 2 . NEW SEIUES. 19

264 P. H. EDGE WORTH.

part into the arytenoideus, and the ventral part into thethyro-arytenoideus and lateral crico-arytenoid." Accordingto Croppert, the crico-arytenoideus posticus is the homologueof the dorso-laryngeus of Amphibia, the other intrinsicmuscles representing the sphincter and laryngei dorsalis andventralis of Amphibia.

TEXT-FIG. 72.

Text-figs. 72, 73.—Gallus, embryo four days. Text-fig. 72 throughthe first branchial, Text-fig. 73 through the second branchialsegment.

Frazer states that in man the thyroid cartilage is developedsolely in the second branchial segment, i. e. it is the secondbranchial bar only, whereas in Echidna (Goppert) a thirdbranchial bar is also formed.

The crico-thyroideus, according to Frazer, is developed

MORPHOLOGY OF CRANIAL MUSCLES IN SOME VERTEBBATES. 265

from the second branchial pharyngeal constrictor; this con-firms the opinion of Furbringer.

The pharyngeal musculature extends forwards into themandibular segment in 13 mm. embryos (Text-fig. 94) ; in14 mm. embryos the anterior end becomes separated, formingthe tensor palati, and in 16 mm. embryos the next succeedingportion forms the levator palati.

TEXT-FIG. 73.

7 3 .

According to Futamura, as stated above, the Anlage of thepalatal muscles of man is at first one "with that of the tensortympani, and is derived from the platysma faciei. I havefailed in verifying this in the rabbit; the platysma faciei inthat animal remains superficial, and the Anlage of thepalatal muscles when first visible was quite distinct fromthat of the tensor tympani, which is cut off from the innerlimb of mandibular myotome.


These phenomena afford an explanation of the innervationof the palatal muscles Ly the Xl th medullary.

MUSCLES DEEIVED FROM TRUKK-MYOTOMES PASSING TO THK

UPPER ENDS OF THE BRANCHIAL BARS.

Vetter described a subspinalis and interarcuales muscles in

TEXT-FIG. 74.

7 4 .

Gallus, embryo 4 | days, transverse section.

Selachii. Fiirbringer subsequently showed that the sub-spinalis and upper interarcuales (which he re-named " inter-basales " ) , were innervated by the spino-occipital nerves, andhe classed them together as "epibranchial spiual muscles."The lower interarcuales (second and third interarcuales ofVettei-)j h e called " arcuales dorsales."

Observation of the development of these muscles confirmsFiirbringer's theory of their nature. The subspinalis and

1 Beevor and Horsley.

MORPHOLOGY OI-1 CRANIAL MUSCLES IN SOME VERTEBRATES. 267

first, second, and third1 interbasales of Scyllium are developedin 23 mm. embryos from the first, second, third, and fourthspinal myotomes (Text-figs. 12, 13, 14), by growths from theirventral edges internal to the ganglia of the ninth and tenthnerves.

A retractor arcuum branchial ium dorsalis is found insome Teleosteii (Vetter), e. g . Perca and Cyprinus, in Amia(Allis, Wiedersheim2), and in Lepidosteus (Wiedersheim2),but is not present in Polypterus (Pollard),or in S a l m o fa r io .In Amia the muscle, which is inserted into the third infra-pharyngo-branchial, arises according to Allis from the thirdand fourth, according to Wiedersheim from the seventh andeighth, vertebral bodies. In Lepidosteus the muscle isinserted into the third iufrapharyngo-branchial, and arisesfrom the lateral surface of the third and fourth vertebralbodies (Wiedersheim). The retractor was supposed by Allisand by Wiedersheim to belong to the system of the levatoresarcuum branchialium.

The muscle is developed in Amia from downgrowths fromthe lower surface and lower part of the internal surface of thesixth to thirteenth trunk-myotomes in 8h mm. embryos (Text-fig. 33); these downgrowths form a longitudinal muscle, theanterior end of which grows forward to the third bar. Itsdevelopment in Lepidosteus is similar, taking place, in 12 mm.embryos, from the third to ninth trunk-myotomes.

l, S.LMNAL MUSCLES.3

In Scyllium, van Wijhe stated that the coraco-hyoideuswas developed from ventral prolongations " sowohl des hin-sterstenKopfrnyotomes als die der vorderenRumpfmyotonie,"and that the coraco-brauchiales and coraco-mandibulariswere formed from the walls of the " unpaaren vorderen

1 The third interbasalis, developed in the embryo, is not described inthe adult by Fiirbrmger.

- Retractor laryngis of Wiedersheim.3 This name is used in the sense stated above.

268 Jj\ H. EDCiEWOBTH.

Verlangerung des Pericardiums." ISTeal, in S q u a l a s acan-t h i a s , found that the Anlage of the hypoglossus musculaturewas formed from the fourth to the eighth post-otic myotomesby buds which separate and come to lie ventral to thebranchial basket; they do not fuse into a common cell mass,but show their primary metamerism, the bud from the fourthmyotome coming to lie between the hyoid and mandibularcartilages and forming " in part the Anlage of the propertongue muscles," whilst "the four following myotomic budscome to lie between the hyoid and procoracoid."

I find that in ScyIlium the initial stages of the developmentof the coraco-mandibulavis and coraco-hyoideus are similar tothose of Squa lus acan th ia s , a s stated by Neal. This stageis completed in 16 mm. embryos, and is immediately followedby one (17 mm.), in which the hind end of the primitivegenio-hyoideus, which does not become affixed to the liyoidbar, grows backwards along- the median edge of the coraco-hyoideus towards the shoulder-girdle—forming the coraco-mandibularis (Text-figs. 11, 12, 13).

The coraco-hyoideus of Sahno sa la r (Harrisou) isdeveloped from ventral downgcowths of the second, third,and fourth trunk myotomes, which bend round the pbauyngealregion, and form a longitudinal column, the anterior edge ofwhich extends forwards to the hyoid bar. A similar develop-ment of the hypobranchial spinal muscles takes place inAcipenser, Lepidosteus, Amia, and Salmo, occurring in 8 mm.,8 mm., 7 mm., and 5 mm. embryos respectively, and in eachcase from the second, third,and fourth trunk myotomes. luSahno f a r io and in Lepidosteus the forward growth of theanterior end reaches the hyoid bar only, so that only a coraco-hyoid is formed. In Acipenser and Amia it extends further,to the symphysis, reaching this in 8^ mm. embryos ofAcipenser (Text-figs. 21, 22), and in 8 mm. embryos in Amia.The long column then divides at the level of the hyoidbar into an anterior and a posterior group—the genio-hyoid1

1 Branckio-mandibularis of Vetter and Allis.

MOEPHOIOUY OF OKANTAL MUSCLES IN SOUK 'VEKTEJBJlATJfiS. 269

and coraco-hyoid.1 The posl erior end of the genio-hyoid growsbackwards (Text-figs. 28, 29,-30), and becomes attached, inAcipenser to the third hypobranchial, and in Amia by twotendons, to the second and third hypobranchials and to amedian aponeurosis between the two coraco-hyoidei(Y-shapedtendon of Allis).

In Polypterus, ? species, Pollard described the hypobranchialspinal muscles as consisting of a brauchio-mandibularis s.genio-byoideus extending from the symphysis of the lowerjaw to the first basi-branchial, and oE a coraco-hyoideus whichhad an additional tendon attached to the first cerato-branchial.Fiirbringer described the muscles as consisting of a coraco-maudibularis exteuding from the symphysis to the shoulder-girdle, and of a coraco-hyoideus.

In P o l y p t e r u s s e n e g a ] as (Text-figs. 35, 36, 37), themuscles consist of a genio-hyoideus and a coraco-hyoideus ;the former extends from the symphysis backwards to the levelof the third branchial bar, where it ends by beiug attached tothe third cerato-branchial and by a tendon which passes down-wards and is attached to a little median ossicle lying betweenthe two coraco-hyoidei. The coraco-hyoidens extends fromthe cerato-hyal backwards to the shoulder-girdle, and has notendon passing to the first cerato-branchial.

Grreil stated that the " hypobranchial musculature" ofCeratodus was developed from ventral downgrowths of thethird and fourth myotomes. He apparently included thecoraco-branchiales as well as the coraco-maudibularis andcoraco-hyoideus under this head, as the first-named were notdescribed as developing in the branchial region. It has beenstated above (p. 234) that the coraco-branchiales are developedfrom the lower ends of the branchial myotomes. The hypo-branchial spinal muscle Anla.ge spreads forwards (Text-fig. '69)reaching the anterior extremity of Meckel's cartilage instage 43. The portion in front of the hyoid bar separates

1 Main portion of coraco-arcnalis anterior (Vetter) in Acipenser ;hyopectoralis (McMnrricli), sterno-hyoideus (Allis) in Amia; the term,used above is that of Fiirbringer.

270 h\ H. EDGEWOKTH.

from that behind, and its hind end grows backwards belowthe coraco-hyoidens (Text-figs. 45, 46, 47) to the shoulder-girdle, forming the coraco-mandibularis. The portion behindthe hyoid bar forms the coraco-hyoideus; in stage 63 it ispartially separated into the coraco-hyoideus and abdomino-hyoideus of the adult, o£ which the latter is continuous withthe trunk muscles behind the shoulder-girdle.

In Necturus (Miss Platt) the hypobrauchial spinal musclesare developed from ventral downgrowths of the third, fourth,and fifth post-otic somites, joined by a few scattered cellsfrom the second somite; the genio-hyoideus is formed fromthe third, the sterno-hyoideus from the fourth and fifth.

In Triton there is a similar development from the third,fourth, and fifth trunk myotomes in 6 A mm. embryos.

The hypobranchial spiual muscles of Rana are developedfrom downgrowths of the first and second trunk myotomesin 6 mm. embryos (Text-fig. 57), which bend round the bran-chial region, forming a longitudinal column which reachesthe inferior labial cartilage in 8 mm. embryos. I t dividesopposite the third branchial bar into genio-hyoid and sterno-hyoid.1 The front end of the former is attached to theinferior labial cartilage (Text-figs. 60, 62), and its hind eud tothe hypobranchial plate as far back as the antero-posterior levelof the third branchial bar. In 12 mm. embryos the internalportion of the genio-hyoid is proliferated from the median edgeof the original muscle (Text-fig. 59). At metamorphosis theinferior labial cartilage forms the anterior end of the lowerjaw, and the muscle so retains its primitive attachments. The.front end of the stemo-hyoid becomes attached to the thirdcerato-branchial, and the muscle extends back to the dia-phi-agm. Towards metamorphosis the shoulder-girdle isdeveloped and the sterno-hyoid becomes attached to it, anda little later the omo-lryoid is separated from its externaledge.

In Alytes, Bufo l e n t i g i n o s u s and Pelobates there is no

' Genio-liypobranchialis and diapliragmato-braiicliiulis mediulis ofSclmltze.


proliferation of au intenml portion of the genio-hyoid ; other-wise the condition in the larvae is the same. In Alytes the hiudend of the genio-hyoid is attached to the third cerato-branchial.

In the vabbifc the hypobranchial spinal muscles are formedfrom downgrowths of the first three trunk myotomes in4 mm. embryos (Text-fig. 82). These have separated in 4£mm. embryos, and form a longitudinal column which extendsforwards dorsal to the interhyoideus and iutermandibularis,reaching the anterior extremity of Meckel's cartilage in

8 mm. embryos, and backwards, reaching the area of theanterior limb in 7 mm. embryos. In 13 mm. embryos ithas divided into genio-hyoid and (primitive) sterno-hyoid,tlie adjacent ends of which are attached to the first branchialbar. In 17 mm. embryos the primitive sterno-hyoid hasdivided into tlie sterno-hyoid, sterno-thyroid, thyrohyoid,and oino-hyoid. Tlie first trunk niyotome, from which themost anterior of tlie downgrowtlis above mentioned takesplace, atrophies in 7i mm. embryos, the second and third in9 mm. embryos.

The Houiologies of the Hj^pobranchia l S p i n a lMuscles.—In Amphibia, Sauropsida, and rabbit, the Anlageof the hypobranchial spinal muscles divides into anterior andposterior portions—the genio-hyoid and sterno-hyoid. Theformer extends from the symphysis of tlie lower jaws to thebasi-brauchial or some branchial bar, the latter extendingthence to the shoulder-girdle or sternum. The division takesplace in the neighbourhood of the first branchial bar iuUrodela, Sauropsida, and rabbit; in Ami ran larvee it is atthe level of the third brauchial bar.

In Scyllium, Teleostoini, and Ceratodus, a similar divisionof the Aulage of the hypobranchial spinal muscles takes placeat the level of the hyoid bar; the hind end of the anteriorportion, which does not gain any temporary insertion to thehyoid bar, then grows backwards ventral or ventro-lateral tothe posterior portion (coraco-liyoideus) and becomes attachedto the first (Polypterus, ? species, described by Pollard), orto the second and third (Amia), or third ( P o l y p t e r u s sene-

272 jj'. H. JGDOEWORTH.

galus, Acipenser) branchial bar, or to the shoulder-girdle,forming a coraco-mandibularis (Scyllium, Ceratodus, Poly-pterus ? species, described by Fiirbringer).

The anterior attachment of the genio-hyoid and coraco-maudibularis is to the front end of Meckel's cartilage exceptin Anuran larvas, where it is to the inferior labial cartilage.In Acanthias, where there is an inferior labial cartilage(Gaupp), the coraco-maudibularis is not attached to this butto Meekers cartilage. In Callorrhynchus (Fiirbriuger) thereis a coraco-prasmaudibularis developed, attached anteriorly tothe inferior labial cartilage.

Fiirbringer lioraologised the genio-hyoideus with thecoraco-mandibularis of Selachii, and supposed that tlioformer was derived from the latter, by giving up its attach-ment to the shoulder-girdle, and gaining a new one to (morerostally lying) portions of the hyobranchial skeleton. Sucha deduction was a legitimate one from the evidence of adultanatomy only, though the alternative was possible, andthe embryological history of the muscles shows that it isthis alternative which occurs; the condition in Teleostouii,Elasmobranchs, and Ceratodus is a secondary one.

The method of development of the hypobranchial spinalmuscles in Scyllium lends additional interest to, and receivescorroboration from, some anatomical facts described by Vetterand Fiirbringer. The degree of backward extension of thecoraco-mandibnlaris towards the shoulder-girdle varies, evenamougst the Selachii. Thus in Heptanchus and Scyllium itdoes not reach the coracoid, whereas in Laemargus andPriouodon it does. Further, the coraco-mandibularis is notcrossed by tendinous inscriptions, in this forming a markedcontrast to the coraco-hyoideus, alongside of which it lies.The only possible exception to this among the forms depictedby Fiirbringer is Cestrastion, and this is probably an apparentone only; it is possible that the tendinous inscription reallyseparates the coraco-hyoideus from the coraco-mauibularis,which only reaches the coracoid by its median edge.Similarly, according to Fiirbringer, there are three tendinous


inscriptions in the cerato-hyoideus of Ceratodus, whilstthere is only one doubtful one in the coraco-mandibularis;1

in Protopterus there are two in the coraco-hyoideus, none in

TEXT-FIG. 75.

75.

TEXT-PIG. 7t>.

at^.cnJ

76-

Text-figs. 75-77.—Rabbit, embryo 3 mm. Text-fig. 75 is throughthe premandibnlar Anlage, Text-fig. 76 through the mandibnlarsegment, Text-fig. 77 through the hyoid segment.

the coraco-mandibularis; in Polypterus ? species there aretwo in the coraco-hyoidenSj none in the coraco-mandibularis.

1 It was not apparent in stage 63 (vide Text-fig. 45).

274 k\ H. EDCEWOBTH.

Again, there are two inscriptions in the coraco-hyoid ofAmia (Allis), and Acipenser (Vetter), none in the genio-liyoid.

The non-development of a genio-hyoid, even as an atrophy-ing Anlage, in Lepidosteus and Salmo would appear, oncomparison with other forms, to be a secondary condition.

The developmental history of the hypobranchial spinalmuscles suggests that their Anlage was primitively anundivided column, extending forward to the symphysis of

TEXT-FIG. 77.

77.

the jaws, an anterior prolongation of the rectus system of thetrunk into the head segments. This divided into genio-hyoid and coraco-hyoid. In fishes the genio-hyoid secon-darily extended backwards, overlapping the coraco-hyoid invarying degrees.

The Anlage of the hypobranchial spinal muscles is formedfrom downgrowths oE several—two or more—trunkmyotomes, that from the foremost myotome taking part inits formation extending furthest forward, that from the nextsucceeding it, and so on. There is a certain correlationbetween the number of trunk myotomes taking part in the


formation of the hypobranchinl spinal muscles and thenumber of trunk-segments included in the skull (vide table,p. 299). In general, the less the number of trunk-segmentsincluded in the skull, the greater tendency there is forthe most anterior trunk inyotomes to take part in theformation of the hypobrauchial spinal muscles, and the lessthe number of anterior trunk myotomes atrophyiug withouttaking part in their formation. The table also shows thatthe hypobranchial spinal muscles are derived from a variablenumber of trunk myotomes. The number varies from two(Rana) to five (Scyllium). Derivation from the smallestnumber is probably the most primitive condition. The numberdoes not vary with that of the trunk-segments included inthe skull, nor with the number of head-segments.

LINGUAL MUSCLES.

The researches of Gegenbaur and Kallius in Salamandrinahave shown that the geuio-glossus is developed from thegenio-hyoideus and the sterno-glossus from the sterno-hyoideus ; the former ends between the lingual glands whichform the fore part of the tongue, and is " also ein DriisenMuskel" (G-egenbaur) ; the latter becomes attached to a plateof dense connective tissue which probably develops at the siteof fusion of the primitive tongue with the glandular portion.Kallius has also shown that in the Anura the genio- and hyo-glossus are developed from the genio-hyoid. The genio-glossus grows towards the subsequently glandular, precopularfield, and later, the hyo-glossus fibres cross those of thegenio-glossus.

To this may be added that in Rana the genio- and hyo-glossus are developed from the inner division of the genio-hyoid, which (vide p. 270) is proliferated from the inner sideof the primitive muscle.

In 27 mm. larvae of Alytes the genio-glossus ends freebeneath the mucous membrane of the precopular field, andthe hyo-glossus passes forward at first below and then lateral


to the long forward projecting basihyal (Text-fig. 63), andis attached to it near its anterior end. In larvse of Bufo,Raua, and Pelobates the hyo-glossus is not attached to therudimentary basihyal.

The development of the lingual muscles oE Lacertamural is has also been investigated by Kallius. The develop-ment of the lingual muscles in other groups of Sauropsida(loc. cit.) showed that the primitive condition of the lingualmuscles is a genio- and hyo-glossus, both developed from

TEXT-FIG. VS.

v," Ay. •

78.Rabbit, embryo 3} mm., longitudinal vertical section.

the genio-hyoid, attached to the long basihyal, the formerto its front end, the latter to its side; and that extensioninto the tongue is a secondary phenomenon.

The condition of the hyo-glossus of Alytes is of interestwhen considered in relation to that of the lingual muscles ofSauropsida. Gegenbaur was of opinion that " die Musku-larisirung scheint vorwiegend im Dienste der Drusen zusfcehen." An alternative hypothesis suggested by the con-dition in Alytes larvte would be that the condition in Saurop-sida is the primary one, and that their functions as glandularmuscles in Amphibia is correlated with the absence (e.g.

SrORPHOLOOSY OF CRANIAL MUSCLKS IN SOME VERT REBATES. 277

TEXT-FIG. 79.

7 9 .

Rabbit embryo 3} mm. The upper part of the section is posteriorto the lower.

TEST-PIG. 80.

8 0 .

Rabbit, embryo 3£ mm. The right side of the section is a littleanterior to the left, which passes tbrongh the second branchialmyotome.

278 .F. H. EDGEWOETH.

Triton) or rudimentary couditioa (e.g. Rana_. Pelobates,Bufo) of the basihyal.

In the rabbit the Aulagen of the lingual muscles are formedfrom the anterior part of the Anlage of the hypobranchialspinal muscles, i . e . from the future genio-hyoid, in 9 mm.embryos, that of the genio-glossus and lingualis by upwardgrowth) that of the hyo-glossus and stylo-glossus by an out-

TEXT-FIG. 81.

<Aov. o o v —

Text-figs. 81-83.—Babbit, embryo 4 mm. Text-fig. 81 is throughthe hyoid segment, Text-fig. 82 through the fourth gill-cleft,Text-fig. S3 through the third branchial gill-cleft.

growth directed upwards and laterally (Text-fig. 91). In 13mm. embryos these muscles have separated from the genio-hyoid, and become distinct (Text-figs. 94, 95).

SOME PHYLOGENETIC CONSIDERATIONS.

The probable phylogenetic relationships of the variousVertebrate groups are determined by the total morphological


TEXT-MO. 82.

8 2 .TEXT-FIG. 83.

63 .VOL. 5 6 , PART 2 . NKW SERIES. 20


evidence available. The cranial muscles form one item onlyof such evidence, but it is of interest to inquire how far theirmorphology falls iu with generally received opinion, and inwhat direction it points in cases where opinions vai-y.

Such an inquiry is beset by the difficulties which arisefrom—(A) secondary innervation of muscles; (B) develop-ment of similar changes in various groups ; (c) atrophy, andnon-development of muscles.

(A) Comparison of the development and innervatiou of thecranial muscles shows that although, in general, a muscle isiunervated by the nerve corresponding to its segment oforigin, yet this is not invariably the case. Thus :

(1) The posterior part of the intermandibularis of Tritonis innervated by the Vl l th (Driiner).1

(2) The intermandibularis of Selachians is, in part, e .g .ScyIlium (Vetter), or wholly, e .g . Acanthias (Vetter), inner-vated by the Vll th .

(3) The intermandibularis anterior and posterior (the lattercalled " inferior genio-hyoid" by Allis) of Amia are innervatedby both the Vth and Vll th (Allis).

(4) The hyo-maxillaris of Teleostomi, developed in thehyoid segment, is in some, e .g . Menidia (Herrick), wholly in-nervated by the Yl l th ; whereas in others, e .g. Bsox (Vetter),Salmo, its hinder part is innervated by the Vl l th and its forepart by the Vth ; and in Amia (Allis) it is innervated by theVth and Vll th.

(5) The anterior digastric of man, pig (Futamura), andrabbit, developed in the hyoid segment, is iunervated by theVth.

(6) The cerato-hyoideus externus of Urodela, developed inthe hyoid segment, is innervated either by the Vll th, e. g.Necturus (Miss Platt), or by the IXth, e . g . Triton (Driiner).

(7) The interarcuales ventrales of Urodela are innervatedboth by the nerves corresponding to their segments of originand also by those of the next anterior segments (Driiner).

(8) In some Teleostomi, e. g. P o l y p t e r u s senega lus ,1 Roman numerals denote cranial nerves.

MOEPHOr.OGY OF CRANIAL MUSCLES IN SOME VERTEBRATES. 281

Esox (Vetter), Meuidia (Herrick), Amia (Allis), Lepidosteus'the only coraco-branchialis present, developed from the mostposterior branchial segment (fourth or fifth), is innervated bythe Xth ; whereas in others, e . g . Amieums (Wright), Salmo(Harrison), it is innervated by the spino-occipital nerves.

(9) The coraco-branchiales of Acipenser, Ceratodus, andScyllium, developed in branchial segments, are innervatedby spino-occipital nerves (Vetfcer, Fiirbringer). The spino-occipital nerves also innervate the four coraco-branchiales ofPolypterus (?) species, described by Fiirbringer.

(10) The capito-dorso-clavicularis of L a c e r t a a g i l i s ,developed from the primitive trapezius, i . e . from branchialsegments, is innervated by spiual nerves (ITurbringer).

(11) The cucullaris, i. e . trapezius, of Gallus, developedfrom branchial segments, is innervated both by the Xlthand by spinal nerves (Fiirbringer).

(12) The trapezius and sterno-mastoid of the rabbit,developed from branchial segments, is innervated both bythe Xl th and by spinal nerves.

(13) The retractor arcuum branchialium dorsalis of Amiaand Lepidosteus, developed from trunk myotomes, is inner-vated by the Xth (Allis, Wiedersheim).

(14) The hinder part of the hypobranchial spinal musclesof the rabbit, which are developed from the first three spiualmyotomes, are innervabed by more posterior spinal nerves.

(15) The interarcualis ventralis I, i . e . branchio-hyoideusor branchio-niandibularis of Sauropsida, is innervated by theXllth.

Fiirbringer held that " Die Innervirung der Muskelndmch bestimtnte jSTerven ist das wichstigte Moment fur dieVergleichung." In criticism of this theory, Cunninghamgave instances from the myology of the trunk and limbs inwhich this criterion failed, and concluded that the nervesupply is "not an infallible guide" for determination of thehomology of a muscle. The above-cited observations showthat developmental phenomena should be taken into con-sideration.


The first fourteen of the phenomena recorded appear to bereferable to a common cause ; if a muscle spreads into one ormore neighbouring segments, that portion tends to be inner-vated by the corresponding nerve or nerves. The backwardextension of the origin of the Xlth appears to be referableto the same cause.

It is not yet known what happens within the centralnervous system—whether there is a corresponding migrationof motor neuroblasts or whether new ones are locally formed.

The cause of the phenomenon cited under (15) above ismuch more obscure. The muscle is the interarcualis ven-tralis of the first branchial segment, and is homologous withthe similarly developed muscle of Amphibia, some Teleos-tomi, and some Mammalia, and yet, unlike them, it is inner-vated by spino-occipital nerves and not by the IXth, just asif it were a coraco-branchialis I.

(B) The possibility of the independent development ofsimilar secondaiy changes in the various groups arises in thecase of the hypobranchial spinal muscles, the hypobranchialcranial muscles, the levatores arcnum branchinlium, andtrapezius, the hyoid bar and related muscles, the adductormandibulas.

In Ceratodus and in Scyllium the hind end of the genio-hyoid secondarily extends backwards to the shouldei--girdle.The question arises whether this feature is inherited from acommon ancestor . or whether it has been independentlyacquired. In favour of the second view are the facts thatwithin the group of the Teleostomi all conditions existbetween that of a genio-hyoid which has slightly extendedbackwai'ds and a coraco-mandibularis.

A similar question arises in regard to the formation ofcoraco-branchiales in Ceratodns and Scyllium. Again, withinthe group of the Teleostomi all variations exist between inter-arcuales ventrales and their homologues, coraco-branchiales.

These secondary modifications in the hypobranchial-spinaland hypobranchial-cranial muscles appear to be morpho-logical expressions of an increased need of tying the


mandibulo-hyo-branohial skeleton to the shoulder-girdle,and the change of function of the latter group of muscles toone similar to that of the former tends to bring about asecondary iimervation from spinal nerves.

A similar question arises in connection with the presenceand absence of levatores arcuurn bianchialium. It has beensuggested above that their absence and the related methodof formation of the trapezius are secondary phenomena

TEXT-FIG. 84.

8 4 .Babbit, embryo 4 mm., longitudinal vertical section.

(p. 257). If so, it is possible that this has been indepen-dently acquired in Scyllium, Sauropsida, and rabbit.

In Scyllium and the Teleostorni a stage of developmentoccurs in which there is a short hyoid bar like that ofAmphibia with a levator hyoidei, which is succeeded by onein which the bar extends up to the periotic capsule. Therelationship of the muscles and of the facial nerve to thelater formed portion of the bar are so different in Scyllium

284 F. H. BDGEWORTH.

and Teleostomi that possibly the only common feature is the

above-mentioned first stage. In Ceratodus, Sauropsida, and

rabbit the hyoid myotome is external to the upper part of the

hyoid bar, as in Scyllium.

In Sauropsida and certain Teleostomi the adductor man-

dibulfe divides into internal and external portions, but in

Teleostomi there is no uniform upgrowth of the external

TEXT-FIG. 85.

8 5 .

Text-figs. 85-87.—Rabbit, embryo 5 mm.; Text-fig. 85 is throughthe first branchial segment, Text-fig. 86 through the thirdbranchial segment, Text-fig. 87 just behind this.

portion to the skull as in Sauropsida. Both division andupgrowth have been independent occurrences in these twophyla.

C. Amongst the animals investigated there are but few inwhich muscle-Anlagen are developed and then atrophy. TheMm. marginales and interarcuales ventrales of the larva ofRana, certain muscles of metamorphosing Urodela describedby Driiner, the levator maxillse superioris of Chelone and

MORrHOLOGY OF CRANIAL MUSCLES IN SOME VERTEBRATES. 285

TEXT-FIG. 86.

6 6 .

TEXT-FIG. 87.

87.

286 p. H. EDGEWORTH.

Alligator, and the genio-byoid of Gallus, were the only onesfound. Otherwise if a muscle is not present in the adult itis not formed during development.

There are certain instances in which comparative evidencesuggests that ancestors probably possessed muscles which arenow no longer developed, even as Anlagen. Such are thegenio-hyoid of Lepidosteus and Salmo, certain Mm. trans-versi ventrales in Amphibia and Teleostomi, the first twoobliqui ventrales in P o l y p t e r u s s enega lu s , thehyo-maxil-laris inSelachii andSauropsida,the levatoresarcuum brauchia-lium in Selachii, Saui-opsida, and Mammalia.

Consideration of the changes which take place in theAnlagen of the cranial muscles in the various Vertebrategroups suggests that the most important are those occurringin the myotouae of the mandibular segment. In Amphibiaand Ceratodus it does not, whilst in Teleostomi, Selachii, andSauropsida it does divide into parts above and beiow thepalato-pterygoid or pterygoid process of the quadrate. Ithas been stated above that the embryological phenomenasupport the view that the second condition has been derivedfrom the first. In the rabbit the quadrate (incus) has nopterygoid process, and the myotome—as in Amphibia andCeratodus—does not divide into upper and lower parts.

Changes take place in the Anuran tadpole, in the form ofthe palato-quadrate bar and in certain muscles in associationwith the development of a suctorial mouth, i .e. the back-ward elongation of the mandibular muscles, the developmentof a submentalis and mandibulo-labialis, the origin of theorbito-hyoideus, or of this and the suspensorio-hyoideus, andthe partial origin of the first branchial levator from thepalato-quadrate bar, the division of the hyo-maxillaris andattachment of one or two of its parts to the palato-quadratebar. As the condition before these events takes place isvei'y like that of an embryo of Ceratodus or an Urodela.n,it would appear probable that the changes are secondarylarval ones and not ancestral.1

1 The difficult question as to the origin and nature of the larval

MORPHOLOGY OF CRANIAL MUSCLES IN SOME VEETBBEATBS. 287

On the other hand, the existence of a hyo-maxillavis and ofMm. marginales, the insertion of the orbito-hyoideus or ofthis and the suspensorio-hyoideus to the cerato-hyal, and theorigin of the trapezius from the skull, are primitive featureswhich are not developed or soon modified in Urodelandevelopment.

In the Urodela the insertion of the levator hyoidei istransferred, wholly or partially, from the hyoid bar toMeckel's cartillage early in development, and the hyo-maxillaris Anlage forms a ligament. The development ofgill-muscles from Anlagen which are homologous with thosewhich give rise to the Mm. marginales of Anuran larva) andCeratodus, and of a cerato-hyoideus externus, are featui'especuliar to Urodela.

Ceratodus resembles Selachii and some Teleostonii, anddiffers from Amphibia in the backward growth of the genio-hyoid to the shoulder-girdle, and in the formation of coraco-branchiales. Ceratodus resembles Selachii and Teleostotnauembryos, and differs from Amphibia in the backward growthof both hyoid myotome and iuterhyoideus, resulting in theformation of a continuous dorso-veutral sheet, C2vd, behiudthe hyoid bar. Ceratodus resembles Teleostomi and Amphi-bia, and differs from Selachii in the formation of levatoresarcuum brauchialium and in the development of the trapeziusfrom a levator. Ceratodus resembles Amphibia, and differsfrom Selachii and Teleostonii in the non-division of themandibular myotome into upper and lower portions. Cera-todus resembles Anuran larvas in the simple condition of theMm. marginales,and Urodela in the ligamentous condition ofthe hyo-maxillaris.

According to K. Fiirbringer, " Wenn wir somit keinebestitnmte Ordnuug der Amphibia von den D i p n o e r na b l e i t e n k o n n e n , so ergiebt sich daraus kein Einwandgegen eiue Abstammung von den D i p n o e r n i ibe r -

condition of tlie suctorial mouth and jaws in Anuran larvse wasdiscmssed by BaJfonr and by Gaupp, though without reference to themuscles.

288 I'. H. EDGEWO.RTH.

h a u p t . . . . " The development,however,iu Ceratodus,ofa coraco-mandibularis, of coraco-branchiales, of a hyoman-dibula, and of a dorso-ventral sheet C3vd behind the hyoidbar, are all secondary to more primitive conditions present inAmphibia.

Goodrich was of opinion that " the Dipnoi are probably aspecialised offshoot from the Teleostoman stem which

TEXT-FIG. 88.

88.Babbit, embryo 7 mm., longitudinal vertical section.

acquired an autostylic structure before the hyomandibulahad become very large and before the hyostylism had becomefully established." The non-division of the mandibularmyotome and the persistence of the dorso-ventral sheetCcjvd are, however, more primitive features than exist inTeleostomi; and in the embryo of Ceratodus there isa liyomandibula, the relations of which are different fromthose occurringin Teleostomi.


Graham Kerr's opinion was that " the Teleostomes theDipnoans and the Amphibians have arisen in phylogeny froma common stem . . . "

Kellicott's statements that " the resemblances iu tlievascular system between Oeratodus (the most primitive of theliving Dipnoi) and the Amphibia, especially Urodela, arenumerous and fundamental and cannot be explained asparallelisms," and that ( fmost of the Blasmobranchcharacters are parallelisms, some of them actually beingpreceded by Amphibian conditions (e.g. the carotid arteries) "are also true of the cranial muscles.

Consideration of the common features in the cranialmuscles of Teleostoman embryos leads to the probability thatsome remote ancestors possessed—a mandibular myotomedivided into upper and lower par t s 1 ; a levator hyoidei, which,owing to the upgrowth of the hyoid bar to the perioticcapsule, was inserted into the inner or posterior surface of ahyomandibula; a dorso-veutral sheet in the opercular fold,divided into a M. opercularis and a constrictor operculi; aseries of levatores arounm branchialium; a trapezius developedfrom the fourth levator; a series of Mm. marginales not fusedwith the transversi ventrales; a series of hypobranchial-cranial muscles consisting of interarcuales ventrales and of acoraco-branchial] s attached to the last branchial ba r ;hypobranchial-spinal muscles, consisting of a coraco-hyoideus,and of a genio-hyoid, the hind end of which had grown backto some more posterior branchial bar overlapping the coraco-hyoideus.

All these features, with five exceptions, may be supposedto have characterised primitive Amphibia ; and these excep-tions, viz. division of the mandibular myotome, formation ofa M. opercularis, aud of a coraco-branchialis, backwardgrowth of the genio-hyoid, upward extension of the hyoid

1 On the supposition that the protractor hyomandibularis of Aoi-penser is a case of atavism in its non-division into levatov aicuspalutius and dilatator operculi, this division of the levator maxillassuperioris would have once characterised the whole group.

290 L<\ H. EDGEWOETH.

TEST-FIG. 89.

90.Text-figs. 89 and 90.—Rabbit, embryo 7J mm.; Text-fig. 89 through

the hyoid segment, Text-fig. 90 through the neck.

MORPHOLOGY OP CRANIAL MUSCLES TN SOME VERTEBRATES. 291

bar to the periotie capsule—are, as shown by their develop-ment, modifications of more primitive features existing inAmphibia.

These phenomena may be considered as additional argu-ments in favour of the theory of a descent of Teleostei, asadvocated by Assheton, from a proto-amphibian stock ; andof Teleostomi in general, as advocated by Graham Kerr, froma stem common to the Teleostomi, Dipnoi, and Amphibia.

In the condition of the cranial muscles Teleostei do notshow any closer resemblances to Amphibia than do othergroups of the Teleostomi.

The curious fact that the trapezius is developed from thefourth levator arcuuni branchialium in Acipenser, Lepidosteus,Amia, and Salmo, though there are five branchial segments,suggests that ancestors of the Teleostomi may have had, likeAmphibia, only four branchial segments, and that an increaseto five took place within the group.

In the possession of only four branchial segments, ofinterarcuales ventrales I, II, and III, of obliquii ventralesnot fused with transversi ventrales, and of very primitivelaryngeal muscles, Polypterus seuegalus shows closerresemblances to Amphibia than do the other Teleostomiexamined.

The main characteristics of the cranial muscles of Selachiiare: (1) Division of the mandibular myotome into levatormaxillae superioris and adductor mandibulte; (2) greatbackward extension of the intermandibularis below theinterhyoideus; (3) non-formation of an opercular fold;(4) upgrowth of the hyoid bar internal to the hyoid myotome,which, originally forming a levator hyoidei, becomes insertedinto its external surface (hyomandibula, or this andceratohyal); (5) non-formation of a hyo-maxillaris; (6)extension backwards of hyoid myotome and interhyoideusforming a dorso-ventral sheet O3vd behind the hyoid bar,though not in an opercular fold; (7) non-formation oflevatores arcuum branchialum; (8) formation of a trapeziusfrom the upper ends of all the branchial myotomes; (9)

292 F. H. EDGBWOETH.

formation of subspinalis and interbasales from anterior trunkmyotonies; (10) formation of coraco-branchiales; (11)formation of adductors from the portions of the branchialmyotomes which lie internal to the branchial bars ; (12)formation of arcuales dorsales, interbranchials, and superficialconstrictors from the portions of the branchial myotomeswhich lie external to the branchial bars; (13) non-formationof transversi ventrales; (14) extension backward of thegenio-hyoid, forming a coraco-raandibularis. Of thesefeatures, (3) (9) and (12) occur in Selachii and them only.

The great development of the branchial musculature,external to the branchial bars, is correlated with the absence,probably the loss, even in developmental stages, of ancpercular fold. It is of interest to note that in Ohimasra(Vetter) (1) a hyo-maxillaris (hyoideus inferior) is present;(2) the dorso-ventral sheet C2vd is situated in an opercularfold; (3) the branchial musculature, external to the bars,consists of simple vertical muscles ("interbranchials" ofVetter), which are similar to the Mm. marginales of Anuranlarvee and Ceratodus, and to the dorsal portions of the obliquiventrales of Teleostomi.

According to Graham Kerr, "the Teleostomes, theDipnoans, and the Amphibians have probably arisen inphylogeny from a common stem, which would in turnprobably have diverged from the ancestral Selachian stock."Fiirbringei-'s theories in regard to the hypobranchial musclesand the neocranium, and Ruge's respecting the facialmuscles, are also based on a similar theory.

Consideration of the morphology of the cranial musclesleads to some doubt on this question. The embryology ofeach group of cranial muscles, mandibular, hyoid, branchial,hypobranchial-cranial, and hypobranchial-spinal, suggeststhat the conditions found in Selachii are secondary to thosewhich may be supposed to have characterised Amphibianancestors—are modifications of a proto-amphibian type.Certain of these modifications occur in other groups also: thusdivision of the mandibular myotome into upper and lower


parts also occurs in Teleostomi and Sauropsida; backwardextension of both hyoid myotome aud interhyoideus to forma dorso-ventral sheet also occurs in Oeratodus aud Teleo-stomi (though in these, in an opercular fold) formation of

TEXT-FIG. 91.

KuoLd. uox

Text-figs. 91-93.—Rabbit, embryo 9 mm.; Text-fig. 91 throughthe mandibular segment, Text-figs. 92 and 93 through thehyoid segment.

coraco-branchiales and of a coraco-mandibularis also occursin Ceratodus and some Teleostomi; non-formation of levatoresarcaum branchialiuin, and the associated method of develop-ment of the trapesrius occurs in Sauropsida and rabbit.

294 F. H. BDGBWOETH.

The significance of such resemblances from a phylogeneticpoint of view is doubtful, though probably the first twonamed are by far the most important.

The ancestry of Mammals has been the subject of inquiryand speculation for many years. Two theories have been

TEXT-FIG. 92.

9 2 .

held—one, that Mammals are descended from Sauropsida,the other, that they are descended from Amphibia.

As regards the cranial muscles, Mammals resembleAmphibia, and differ from Sauropsida in the followingparticulars: non-division of the mandibular myotome intodorsal and veutral parts, formation of a hyo-maxillaris(anterior digastric), non-formation of a dorso-ventral sheet


Cavd in the hyoid segment, innervation of the interarcualisventralis I (branchio-hyoideus) by the IXth.

On the other hand, Mammals resemble Sanropsida, anddiffer from Amphibia, in the non-formation of levatoresarcuum branchialium, aud the associated development of the

TEXT-FIG. 93.

kU»SvsW*n.atexk ouL

9 3 .

trapezius from the upper ends of all the branchial myotomes,disappearance of the branchial myotomes (after formation oftrapezius and interarcuales ventrales from their upper andlower ends), non-formation of transversi ventrales.

It has been suggested above in discussing individual groupsof muscles that all the first-named features are primary ones,and that all the second-named features are secondaryphenomena. It is possible that secondary features may have

VOL. 5 6 , PART 2 . NEW SERIES. 2 1

296 F. H. EDGEWOKTH.

been independently acquired; thus the absence of levatoresarcuum branchialium and method of formation of thetrapezius also occurs in Selachii. The morphology of thecranial muscles is thus in favour of an Amphibian ancestry ofMammals. In the attachment of the posterior digastric tothe hyoid bar, and not to the lower jaw, some Mammals

TEXT-FIG. 94.

U.bol.

9 4 .Text-figs. 94 and 95.—Rabbit, embryo 13 mm.; transverse sec-

tions through the mandibnlar segment. Text-fig. 94 is themore anterior.

present a more primitive feature than is found in auy adultAmphibia. A descent from a proto-amphibian stock is thussuggested.

The ancestry of Sauropsida has been the subject of butfew speculations. Furbringer was of opinion that "Diestrepto-stylen Pro-reptilia aber haben sich neben den strepto-stylen Pro-mammalia auf tiefer' stehenden streptostylen

MORPHOLOGr OF CRANIA!, MUSCLES IN SOME VERTEBRATES. 297

Thieren entwickelb welche im Grade ihrer AusbildungamphibienartigeThieregleichznsetzen sind. . . ." GrahamKerr's opinion was that "the ancestors of the Amniotaprobably diverged about one or several points from theregion of the stem common to Dipnoi and Amphibia."

As regards the cranial muscles, the differences between

TEXT-FIG. 95.

Lf\XeA,nv O*nA.

d^t.iltd.

9 5 .

Sauropsida and Amphibia have been mentioned above. Inthe division of the mandibular myotome into upper andlower portions, and in the formation of a ventro-dorsal sheet,C3vd, in the hyoid segment, Sauropsida resemble Selachii andTeleostomi, and also as regards C3vd, Dipnoi. The shiftingof insertion of the levator hyoidei from cerato-hyal toMeckel's cartilage and the morphologically primitive con-dition of the hypobranchial spinal muscles are common toboth Saiu'opsida and Amphibia.


ON FURBRINGER'S THEORY OF THE SKULL.

It is of interest to inquire whether the above suggestionsas to the phylogeny of various groups of Vertebrates receiveany support from the morphology of the skull.

According to Fiirbringer's theory the portion of the craniumin front of the exit of the vagus is the original cranium—thepalfeocranium. The neocranium has been formed by theaddition of spinal skeletal elements, which originally werefree. This took place in several stages ; in the first a proto-metamer neocranium is formed—present in Selachii andAmphibia. The union of further additional elements bringsabout the anximetamer condition of the neocranium, found inhigher fishes and Amniota.

The added spinal nerves—spino-occipital nerves—can bedivided into two categories, the " occipital/' brought in withthe protometamer neocranium, and the " occipito-spinal,"additionally added with the auximetamer neocranium. Thevarying number of spino-occipital nerves is due to'the varyingposition of the cranio-vertebral junction.

The assimilated occipital nerves are indicated by theterminal letters of the alphabet, the assimilated occipito-spinal nerves by the initial letters. Their correspondingmyotomes are given corresponding (larger) letters. By thismethod it is possible to express either or both of two possi-bilities—the reduction of more anterior or the addition ofmore posterior nerves.

The following table, which is taken mostly from Gaupp,shows the results of the investigation of various vertebrates,and a column has been added showing the number ofmyotomes taking part in the formation of the hypo-branchial muscles.

A spinal segment is typically indicated by a somite ormyotome, anterior nerve root, and posterior nerve root. Theresearches of Fiirbringer and other observers have'shown thatas segments are assimilated their nerve roots tend either not


Armra—Pelobates (Sewertzoff) .Rana (Miss Elliott;

Urodela—Siredon (Sewertzoff)Nectnrus (Miss Platt) .

TritonDipnoi—

Ceratodus (K. Filrbringer) .

Protopterus (Agar)

Lepidosiren (Agar)

Mammals—Sheep, calf (IVoriep)Rabbit

Reptilia—Ascalobates (Sewertzoff)Lacerta (Hoffman)

Lacerta (Chiaiugi and v.Bemmelen). .

Birds —Tinnunculus (Suschkin)Uallus

Teleostomi—Amia (Schreiner) .Salmo salar (Wilcox)

T r u t t a f ario (Wilcox)Lepidosteus (Schreiner)Acipenser (Sewertzoff) .

Selachii (Ganpp)—Squalus acaiithias .

Scyllium canicnla .

trunksegmentstaken upinto theskull.

33

23

—

5

3

A

3—

45

4

4

45

57

77

—

Nature of

Recording toFiirbrinjjer's

theory.

Protometamer„

„

—

Anximetamer(Gaupp)

Protometamer(Agar)Ditto

Anximetamer

„

,?

rt,,'„

Protometamer

Taking part in theformation of hjpo-ljranchial spiuiil

muscles.

—

1st, 2nd.

—2nd (few cells),

3rd, 4th, 5th(Miss Platt).

—

2nd 3rd (Greil).

2nd, 3rd, 4th(Agar).

2nd, 3rd, 4th(Agar).

—1st, 2nd, 3rd.

—2nd, 3rd, 4th, Sth

(Hoffman)

—

—1st (few cells),

2nd, 3rd, 4th, 5th.

2nd, 3rd, 4th.2nd, 3rd, 4th(Harrison).

—2nd, 3rd, 4th.2nd, 3rd, 4th.

—4th, r.th, 6th, 7th,

Sth (Neal).4th, 5th, 6th, 7th,

Sth.

to be developed, or after development to atrophy, and thatthis takes place from before backwards. The non-develop-ment or atrophy affects dorsal more readily than ventralroots. Reduction, i.e. atrophy after development, of somites

300 V. H. EDGE WORTH.

or myofcomes comes last. This general rule leads to hesitationin accepting the existence of anterior nerve roots withoutcorresponding somites or myotomes as evidence of assimi-lated segments, e .g . deductions from the observations ufChiarugi and Martin in Mammals.

The theory of Fiirbringer is based on the probability of theprimitive nature of the conditions found in Selachians. Butfrom the foregoing table of the observed number of assimi-lated spinal segments in various Vertebrates it would appearthat the descriptive adjectives applied to some neoerania arenot deserved. As determinated by the number of assimilatedspinal segments the Amphibian neocranium is shorter thanthat of Selachians. It was therefore maintained that theoccipital region of Amphibians corresponds to a lnultiplutn ofspinal segments. The difficulty of doing so is emphasised bythe absence of auy direct evidence in its favour. If themuscles of the head in Amphibians and Selachians be com-pared it is clear that the condition in the former is far moreprimitive than in the latter, and that many cranial musclesof ScyIlium pass through what may be regarded as anAmphibian stage during development; and if the observedfacts in regard to the number of assimilated spinal segmentsbe taken sans p a r t i p r i s the condition of the skull tellsthe same tale. Purbringer states that the junction of theskull and vertebral column is at the same place in Sauropsidaand Mammalia; hence the five occipital nerves in Reptilianembryos are called v, w, x, y, z; and the three in Mammalsx, y, z, so that the last assimilated nerve is the same—z.But in Mammals there appear to be only three assimilatedsomites, in Reptiles four or five. The argument drawn fromthe existence of a pro-atlas is probably of no great weight indetermining the limits of the skull and vertebral column, forin Sphenodon (loc. ci t.) that structure is the persisting costalprocess of the last coalescing vertebra, and the same may betrue in Mammals without there being any but a serial,homology between these last coalescing vertebras.

The conclusion which might be drawn from the number of

MORPHOLOGY Of CRANIAL MUSCLES IN SOME VERTEBRATES. 301

TEXT-FIG. 96.

Text-figs. 06 and 97.—Rabbit, embryo 13 mm., longitudinal verticalsections. Text-fig. 96 is the more external.

302 V. H. E.DGBWOKTH.

coalescing spinal segments in Amphibia, Sauropsida, andMammalia—viz. 2 or 3, 4 or 5, and 3—harmonises with theevidence of the cranial muscles, in which there is a closersimilarity between Mammalia and Amphibia than betweenMammalia and Sauropsida.

A SUGGESTED MORPHOLOGICAL CLASSIFICATION OF THE MOTOR

CENTRES OJ? THE MID- AND HIND-BRAIN IN MAN.

Gaskell divided the motor centres of the cranial nerves

TEXT-FIG. 98.

Pig, enibryo 8 mm., longitudinal vertical section.

into two categories : (1) Somatic, a continuation of theanterior column of the spinal cord, innervating somaticmuscles—Illi-d (external ocular muscles), IVth, Vlth, Vllth(part which arises from the Vlth nucleus), Xllth. (2A)Non-ganglionated splanchnic, a continuation of thelateral column of the spinal cord, innervating voluntary-splanchnic muscles—Vth (motor descending root), Vth(motor), Vllth, IXth, Xth, Xlth (part which arises fromlateral horn). (2B) G-anglionated splanchnic, a con-tinuation of Clarke's column—Illrd (G. ciliare), Vllth (N.

MORPHOLOGY Ol'1 0KAN1AL MUSCXKS IN SOAtE VJilKTEUKATKS. 3 0 3

intermedius with gang, genie), IXth (gang, petros.), Xth,Xlth (gang, trunci vagi), Xllth (gang, hypoglossi).

This classification of the motor centres, as regards those ofvoluntary muscles, followed v. Wijhe's theory of the mor-phology of the cranial muscles. It was also adopted byStrong and by Herrick.

According to Streeter the motor nucleus of the Vth nervein man is developed in the lateral plate, and the nucleusambiguus of the Vllth, IXth, and Xth in the basal plate.

TEXT-FIG. 90.

99.

Pig., embryo 15 mm., portion of longitudinal vertical section.

The issuing fibres of the Vth pass sti-aight outwards likethose of the dorsal efferent fibres of the IXth, Xth, andXlth (medullary) ; whilst those of the Vllth, IXth, andXth, arising from the nucleus ambiguus, have a characteristiccurved path. The motor nucleus of the Vth is a hypei"-trophied representative of the dorsal motor nuclei of theIXth, Xth, and Xlth (medullary), or the latter is representedin the mesencephalic root of the Vth.

Kappers showed that the original position of the Vllth,IXth, and Xth motor nuclei is medio-dorsal, and that the

'304 F. H. EDGEAYOBTfl.

venti'al position of the nucleus ambignus is only found inMammals;, where the importance of the ventral tegmentnrais increased by the pyramidal tract, whilst a part keeps itsoriginal position near the mid-dorsal line because not verymuch influenced by the long descending tracts of the frontalparts of the brain.

It would result from a comparison of these researches thatthe ventral position of'the Vllth nucleus, and of the nucleusambiguns of the IXth and Xth, is a secondary oue, the curvedpath oE their issuiug fibres representing a phylogenetic descentof the "whole or part of their nuclei; whilst the motor nucleusof the Vth has preserved its original position. This positionis a dorso-median one. The nucleus of the Xlth spinaloccupies a more or less lateral position in the cervical cord,but, as shown by the development of the muscles it inner-vates, the nerve is a specialised branch of the Xth, thenucleus of which has extended backwards into the spinal cord.

The following classification of the motor nuclei of thecrania] nerves is a repetition from a neurological point ofview of the theory which has been advanced above concern-ing the morphology of the cranial muscles, and consequentlystands or falls with it.

Somat ic , innervating muscles derived from the inyotornesof the cerebral and three anterior body segments; I l l rd(external ocular muscles), lVth (superior oblique), VIch(external rectus), Vth (temporal, masseter, pfcerygoids, tensortympani, anterior digastric), Vllfch (posterior digastric, stylo-hyoid, stapedius), IXth (interarcualis ventralis I s. branchio-hyoideus, when present), Xth and Xlth medullary (inter-arcualis ventralis I I I s. interthyroideus, in Ornithodelphia),Xlth spinal (sterno-mastoid and trapezius), Xl l th (hypo-branchial spinal muscles, and lingual muscles derived fromthe geuio-hyoid). S p l a n c h n i c , innervating muscles deriveddirectly or indirectly from the walls of the cephalic coelou,i . e . part of motor nucleus of Vth, which innervates mylohyoid;part of motor nucleus of Vllth, which innervates facial andplatysma muscles; part of motor nuclei of IXth, Xth, and

MOKPHOLOtl V OF CRANIAL MUSCLES I>T SOME VERTEBRATES. 305 '

Xl th medullary, which innervates tensor and levator palati,palato-glossuSjStylopharyngeus,pharyngea] constrictor, laryn-geal muscles, crico-thyroid.

The primary cranial uerves are the l l l r d , Vth, T i l t h ,IXth, and Xr,h; the Xth innervating in the rabbit twomyotomes (second and third branchial), the others one esich.The primary dorsal position of their motor nuclei (otherthan that of the l l l r d ) , the dorso-lateral emergence of theirmotor with their sensory fibres, and the relationship—external—of the issuing nerves to the correspondingmyotomes, are related phenomena. If Balfour's theory, thatthe head and trunk became " differentiated from eachother at a stage when mixed dorsal and sensoi"y posteriorroots were the only roots present/ ' be associated withFiirbriuger's theory that the myotomes primitively l»yexclusively lateral to the notochord, it would follow that inthe body region anterior nerve roots were secondarilydeveloped in correlation with the upgrowth of the myotomesto the mid-dorsal line, and the posterior roots became exclu-sively, or almost exclusively, sensory. In the head, wherethis upgrowth does not take place, or to a veiy limitedextent, a more primitive condition persists both in theposition of the motor nuclei and the emergence of theirefferent fibres.

A further, probable, distinction between the somatic musclesof the body and those of the head is that ganglionated muscle-sensory nerve-fibres pass to the former but not to the latter.1

The position of the nucleus of the l l l r d nerve and the pathof its nerve-fibres may be associated with the loss of cutaneoussensory fibres. Evidence of such loss and of a primitive dorso-lateral emergence of its nerve-fibres is found in the observa-tion of Neumeyer that in the twenty-nine and forty-three hoursold chick " derNerf vom dorsalen Theile des Mittelhirns, alsoin der Gegend der Ganglionleiste seinen Ursprung nehme,sich also sekundar mit seinem definitiven Abgangsortvereinige."

1 I hope to give tlie evidence for this in a future paper.


The Anlagen of the superior oblique and external rectusare developed from forward extensions of the upper ends ofthe mandibular and hyoid myotomes, and the IVth and VIthnerves may be regarded as, phylogenetically, late formations.

There do not appear to be any investigations on theexistence of cell-groups in the Vth motor nucleus, whichmight correspond to the somatic and splanchnic musclesinnervated. The nucleus coutains a centre for the anteriordigastric, but it is not known whether this migrates, duringdevelopment, from the facial nucleus, or whether it is locallydeveloped. The fibres oE the Vth mesencephalic root join themotor root (Ca/jal), but it d6es not appear certain whatstructures it innervates.

The motor nucleus of the Vl l th nerve consists, accordingto van Grehuchten and Marinesco, of four cell groups, threeventral and one dorsal : of these, the internal ventral is thecentre for the stapedius, the middle for the auricular muscles,the external for the inferior facial muscles, and the dorsalnucleus for the superior facial muscles (frontalis, corrugatorsupercilii, and orbicularis palpebrarum). According to thisaccount there is no special cell-group for the posteriordigastric and stylohyoid, which seems unlikely. Morerecently, Kosaka has stated that the dorsal cell group in thefowl is the motor nucleus for the digastricus. The subjectevidently needs further investigation.

The glosso-phai-yngeal nucleus, according to v. Geliuchten,consists of a ventral cell-group only; according to Streeterit has a dorsal nucleus as well as a nucleus ambiguus. • Inthe monkey (Beevor and Horsley) it innervates the stylo-pharyngeus and (?) the middle constrictor of the pharynx.It is not kuown whether there is a separate cell-group for thebranchio-hyoid in animals, e. g. pig, dog, where this muscleexists.

The Xfch and Xlth. medullary are primitively, in the rabbit,the nerves of the second and third branchial segments. TheXth efferent fibres arise from dorsal and ventral motor nuclei,those of the Xlth medullary from a dorsal nucleus only (v.

MORPHOLOGY OP CRANIAL MUSCLES IN SOME VERTE1TRAT.ES. 307

Gehuchteu). As all the fibres of the Xl th medullary jointhe Xth, and all the fibres of the Xl th spinal pass to thetrapezius and sterno-mastoid,1 it is a little questionable whetherthe old distinction of the two parts of the accessorius is worthpreserving. The term X l t h or accessorius might well belimited to what is now known as the X l t h spinal. In nMammal like the rabbit, where the whole of the second andthird branchial myotomes (other than their dorsal endswhich take part in forming the trapezius and sterno-mastoid) disappear during development, the Xth and Xl thmedullary motor centres contain none of the original somaticefferent fibres or cell-groups, and their new centres are thoseinnervating muscles derived from cells proliferated from thewall of the cephalic coelom. They also contain motor centresfor certain visceral muscles which are developed in the bodyregion.

The Xth and Xl th medullary centres overlap antero-posteriorly the Irypoglossal nucleus, probably owing to theirbackward extension into the first three segments of thespinal cord.

The Xl th spinal is, as emphasised by Fiirbringer, a truecerebral and not a spinal nerve. I t innervates a specialgroup of muscles which, in the rabbit, are derived from theupper ends of the three branchial myotoraes. Its nucleusof origin is, from a phylogenetic point of view, a backwardextension into the spinal cord of the (dorsal) nucleus of theXl th medullary, but it is not known what happens inembryonic development.

The hypoglossal nucleus is the motor centre of the hypo-branchial spinal muscles, of the rectus system, developedfrom the first three body myotomes. Cell-groups correspondingto the upper, atrophying portions of these myotomes havebeen lost. I t is not known whether the subdivision of thenucleus into the parts with large and with moderate-sizedcells corresponds with individual muscles or muscle-groups.The hinder part of the hypobranchial spinal muscles has a

1 In dog (loc. cit.) and man (Streeter).

308 F. H. EDGE WORTH.

secondary innervation from cervical segments—first, second,and third in man, first and second in the dog—but it isnot known whether this is due to backward migration or tolocal development of motor neuroblasts.

ON THE SIZE OF THE MEDULLATED NERVE-FJBEES PASSING TO

CRANIAL MUSCLES.

Gaskell stated that in the dog1 large fibres, 14-4 to 18 ft indiameter, were present in the I l l rd (external ocular muscles),IVth, Vlth, VTIth (destination not traced), and Xll th.The corresponding muscles were considered to be somatic.Nerve-fibres not exceeding 1O8 n in diameter were found inVl l th (facial muscles), pharyngeal nerves, and recurrentlai-yngeal; and the corresponding muscles were consideredto be splanchnic. Apparently he did not take the size of thenerve-fibres as the sole criterion of the somatic or splanchnicnature of a muscle, for the sterno-mastoid and trapeziuswere considered to be splanchnic, though the nerve (spinalXlth), showed the larger size of nerve-fibres. A furtheranalysis (loc. cit.) of the size of nerve-fibres passing to cranialmuscles in the dog shows that : (1) In any individual nerve,fibres are found of all sizes up to the largest present; (2) thenerve-fibres taper very slightly as they pass from the centralnervous system to the muscles; (3) if comparison be madebetween the maximum size of the nerve-fibres and themorphological nature of the muscles to which they pass, thefollowing results appear: (A) Nerve-fibres of the greatestsize (17*6 /x in diameter,1 in some dogs only 16 /.<), are foundin the nerves of the external ocular muscles, temporal,pterygoids, tensor tyrnpani, digastric (both from Vth andVllth), stylo-hyoid, branchio-hyoid, trapezius, sterno-mastoid, genio-hyoid, sterno-hyoid, sterno-thyroid, thyro-hyoid, and omohyoid—all of which, according to the theory

1 This is also the maximum size of the nerve-fibres in the anteriorroots of the non-liinb portions of the spinal cord. In the limb areas itis slightly greater.

MORPHOLOGY OF CRANIAL MUSCLES IN SOME VEBTEBKATES. 309

advanced above, are somatic in origin, (B) Nerve-fibres of aless maximum diameter (12"8 n, in some dogs only 11"2 ft),are found in the nerves of the mylohyoid, facial and platysrnamuscles, palatal, pharyngeal, arid laryngeal muscles and crico-thyroid — all of which, according to the theory advancedabove, are splanchnic in origin; and also in the nerves ofthe lingual muscles, which are developed from the genio-hyoid—a somatic muscle.

Herrick stated that the nerve-fibres of the branchialmuscles o£ Menidia were characterised by their large size,and supposed—on the theory that these muscles were ofsplanchnic origin — that they had acquired this somaticfeature. On the theory advanced above, however, the bran-chial muscles are somatic in origin.

The small size of the nerve-fibres of the lingual muscles iscurious, but the muscles, though somatic in origin, haveintimate relations to a splanchnic epithelium. This sugges-tion is supported by the measurements of the nerve-fibrespassing to the genio-hyoid and lingual muscles of L a c e r t av i r i d i s and T e s t u d o m a u r i t a n i a ; in the former animalthe maximum diameters found are 11'6 and 9"6 /.i respectively,whereas in the latter animal both maxima are the same, viz.

I have, in conclusion, to express many thanks to Prof.Salensky for embi'yos of Acipenser; to Prof. Bashford Deanfor embryos and for the loan of sections of Ceratodns; to Prof.Graham Kerrfor specimens of P o l y p t e r u s s e n e g a l u s ; andto Prof. Fawcetfc for the loan of sections of the pig; also tothe last-named for much kindness shown to me during man}'years in his laboratory.

LlTEttATURE.

Agar ('08).—" The Development of the Skull and Visceral Arches inLepidosiren and Protopterus,"' ' Trans. Roy. Soc. Edin.,' vol. xlv.(08).—" The Development of the Anterior Mesodemi and Paired

Fins with their Nerves in Lepidosiven and Protopterus/' ' Trans.Roy. Soe. Edin.,' vol. xlv.

310 V. H. EDGE WORTH.

Allis ('97).—'" The Cranial Muscles and Cranial and First Spinal Nervesin Amia Calva," ' Jonrn. of Morph.,' vol. xii.

Assheton ('07).—"The .Development of G-ymnarchus N i l o t i c u s " ;

The work of J. S. Bndgett.

Beevor and Horsley (88).—" Note on Some of the Motor Functions ofCertain Cranial Nerves (Fifth, Seventh. Ninth, Tenth, Eleventh,Twelfth) and of the First Three Cervical Nerves of the Monkey(Macacus sinicus)," 'Proc. Roy. Soc'

Bijvoet ('08).—" Znr vergleichenden Morphologie des Muscuhis digas-tricus bei den Siiugethiere," ' Zeitschr. f. Morph. u. Anthrop.,'Bd. xi, Heft 2.

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VOL. 5Q, PART 2. NEW SERIES. 22


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EXPLANATION OF REFERENCE LETTERS ON THETEXT-FIGURES.

abd. An. Abducens Anlage. An. of sup. obi. Anlage of obliqunssuperior, abd. liyoid. M. abdomino-hyoideus. add. mand. M. adductormandibulae. add. mand. ext. M. adductor mandibulae externus. add.mand. int. M. adductor mandibulee internus. ant. dig. M. digastricus

MORPHOLOGY OF CLtANIAL MUSCLES IN SOME VERTEBRATES. 315

anterior, arcualis dors. M. arcualis doi'salis. aur. temp. n. Auricnlo-temporal nerve, br. add. M. adductor arcus branchialis. br. aor. ar.Branchial aortic arch, hr.bar. Branchial bar. br. my. Branchial myo-tome. branch, h/ijoid. M. branchio-hyoideus. bucc. cav. Buccal cavity.ceph. cod. Cephalic coeloni. cer. br. Cerato-branchial cartilage, cer. hy.any. M. cerato-hyoideus angnlaris. cer. liyal. c. Cerato-hyal cartilage.first cerv. n. First cervical nerve, ccel. Coelom. cons, colli. M. constrictorcolli. cons, operc. M. constrictor operculi. cor. branch. M. coraco-branclnalis. cor. hyoid. M. coraco-hyoideus. cor. mand. M. coraco-nian-dibulai-is. c.:a>elDorso-ventralnmscular sheet inhyoid segment, dil. lury.M. dilatator laryngis. dilat. operc. M. dilator operculi. dor. aor. Dorsalaorta, dorso-lary. M.. dorso-laryngeus. epibr. Epibranchial cartilage, ext.and. meat. External auditory meatus. extra-temp. M. extra-temporal is.Gass. g. Gasserian ganglion, gen. glossus. M. genio-glossus. gen. glossttsand Ungualis an. Anlage of M. genio-glossus and lingualis. gen. hyoid.Genio-hyoid. gill. ni. An. Anlage of muscles of external gill. (j.-c. Gill-cleft, hy. ceph. ccel. Hyoid section of cephalic coelom. hyogloss. M. hyo-glossus. hyogloss. and stylogloss. An. Anlage of M. hyoglossus and M.styloglossus. hyohy. inf. M. hyo-hyoideus inferior. Hyohy. sup. M. hyo-hyoidetis superior, hyoid bar. Hyoid bar. liyoid iny. Myotome of hyoidsegment, hyoid aor. ar. Hyoid aortic arch, hyomax. M. hyoniaxillaris.hyomax. lig. Hyoniaxillaris ligament, hyomand. c. Hyomandibular carti-lage, hypobr. c. Hypobranchialcartilage, hypohyal. Hypohyalcartilage.hypobr. sp. in. An. Anlage of hypobranchial spinal nmscles. ivf. lab.cart. Inferior labial cartilage, interarc. vent. M. interarcualis ventralis.interbas. M. interbasalis. interhyal. Interhyal cai'tilage. interhyoid.M. interhyoideus. intermand. M. intermandibularis. lary. Larynx.lev. br. M. levator arcus branchialis. lev. hyoid. M. levator hyoidei.lev. lab. sap. An. Anlage of M. levator labii superioris. lev. max. sup.M. levator maxillcB supei'ioris. lev. pal. and tens. pal. An. Anlage oflevator and tensor pulatini. Lingualis. M. lingualis. M. inarg. M.marginalis. mand. aor. ar. Mandibular aortic arch, viand, ceph. ccel.Mandibular section of cephalic ccelom. mand. lab. M. mandibulo-labialis.mand. my. Myotome of niandibular segment, mand. seg. Mandibularsegment, mass. M. massetericiis. mylohyoid n. Mylohyoid nerve. Me.Meckel's cartilage, mental n. Mental nerve. N. Olfactory epithelium.nictat. in. An. Anlage of nictating muscles, obliq. dors. M. obliquusdorsalis. obliq. ivf. M. obliquus inferior. obliq. sup. M. obliquussuperior, obliq. vent. M. obliquus ventralis. asoph. const. Constrictorof oesophagus, oper. fid. Opercularfold. orb. hyoid. M. orbito hyoidens.pal. pr. of quad. Palatine process of quadrate, pal. quad. Palato-quadrate, pcd. quad. Me. palato-quadrato-mandibular arch. phar.Pharynx, phar. br. Pharyngo-branchial cartilage, phar. clav. ext. M.pbaryngo-clavicularis externus. phar. clav. int. M. pharyngo-clavicularis


interims, phar. vi. Pharyngeal muscles, platys. colli. Platysma colli.platysina fac. Platysma faciei. platys. oceip. Platysma occipitalis.premand. An. Anlage of premandibular muscles, post, dig., stylohy. andstap. An. Anlage of posterior digastric stylohyoid and stapedius muscles.proa. asc. Processus ascendens of quadrate, proc. has. Processus basalisof quadrate, protr. liyoin. M. protractor hyomandibularis. ptery. M.pterygoideus. quad. Quadrate, quad. ang. M. quadrato-angularis. rec.lary. n. Recurrent laryngeal nerve, red. ext. ]VI. rectns extemus. red.inf. M. rectus inferior, red. int. M. rectus interior, red. sup. M. rectussuperior, retr. arc. br. M. l-etractor arcuum branchialium. retr. bul.bi.M. retractor bvilbi. retr. hymn. M. retractor hyomandibularis. retr.hyom. et operc. M. retractor hyomandibularis et opercularis. scap.Scapula, sh. girdle. Shoulder girdle, spl. meso. Splanchnic mesodevm.st. mast. M. stemo-mastoideus. stemo-hyoid. M. sterno-hyoideus. stylo-gloss. M. styloglossus. stylophary. M. stylopharyngeus. submax. M. sub-maxillaris. subniax. g. snbmaxillary gland, subment. M. subnientalis.suborb. c. Suborbital cartilage, siibteinp. M. subtemporalis. susp. ang.M. suspensorio-angulai'is. temp. M. temporalis. temp, and mass. An.Anlage of M. temporalis external pterygoid masseter. iensor tym,p. M.tensor tympani. track. Trachea, trap. M. trapezius. tr. my. Trunkmyotonie. trans, vent. M. transversus ventralis. vent. aor. Ventralaorta. Roman numerals. Cranial nerves.

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