Appendicular Skeleton

Appendages and supporting girdles

Pectoral Girdle

Function

Pectoral Girdle – Replacement bones

Coracoid(Epicoracoid)ScapulaSuprascapula

Pectoral Girdle – Membrane bones

ClavicleCleithrumSupracleithrumPostcleithrumPosttemporalInterclavicle(Episternum in tetrapods)

Pectoral Girdle

Glenoid fossa on scapula for limb attachment

Key Point

What trend do you see as you look at the overview of pectoral girdles?

Pectoral Girdle - Placoderms

First to have a pectoral girdle

Pectoral Girdle - Chondrichthyes

CartilageNo dermal elementsCoracoid, scapula, suprascapula

(scapulacoracoid)Not connect to axial skeleton, but fused at

midline

Pectoral Girdle – Bony fish

Membrane bonesClavicle, some have interclavicleCleithrum – largestSupracleithrum, postcleithrumPosttemporal – anchors to skull

Pectoral girdle – bony fish

Replacement bones CoracoidScapula

Pectoral Girdle - amphibians

Membrane bonesReducedLose posttemporalEarly amphibians gained an interclavicle as

a brace

Pectoral Girdle - amphibians

Replacement bonesCoracoidScapula and suprascapula

Pectoral Girdle - amphibians

Urodeles have no membrane bones, including clavicle

Anurans have clavicle, no interclavicle and usually no cleithrum

Pectoral girdle - Reptiles

Stem reptiles & synapsidsMany membrane bones presentMost replacement bones presentNew posterior coracoid present

Pectoral girdle - Reptiles

Modern reptiles have scapula, coracoid, sometimes clavicle, sometimes interclavicle

Crocodiles have reduced clavicleTurtles have interclavicle fused with shellSnakes have no girdleLizards have a significant clavicle and

interclavicle

Pectoral Girdle - birds

Furcula (2 clavicles plus interclavicle)Scapula – bladelikeCoracoid (anterior or pro-) which articulates

with sternum

Pectoral Girdle - mammals

Monotremes similar to stem reptilesClavicle in mostScapula

– Coracoid process from posterior coracoid– Spine is new– Acromion process articulates with clavicle (not

new)

Pelvic Girdle

Stability, encloses pelvic cavity organsIn tetrapods, it has three parts called the

ilium, pubis and ischiumWhen these three bones fuse into one, the

fused bone is the innominate or coxal boneAcetabulum is the socket for the thighSymphysis in all but birdsReplacement bone

Pelvic Girdle - Fish

Pelvic plate or symphysis

Pelvic Girdle - amphibians

PubisIlium (long & slanted in frog)Ischium

Pelvic Girdle - Reptile

Sacroiliac joint is stronger and broader for more muscle attachment and stability

Pelvic Girdle - birds

Synsacrum – Ilium is braced against fused vertebrae

No symphysis WHY??

Pelvic girdle - mammals

Epipubic bone in marsupials is unique for pouch support

FINS

Steering, rolling, braking, stabilizers, forward & vertical movement

Fin structure

Skin epidermis coveringFin rays in dermis

– Lepidotrichia (scale-hair) bony dermal scales, segmented

– Ceratotrichia (horn-hair) cartilaginous unsegmented rays

Fin Structure

Skeletal base (cartilage or bone) for supportPterygiophores (bearing fin)Basals are proximalRadials are distal

Paired Fins

Absent in agnathansSome in placoderms & acanthodiansChondrichthyes

– Fin Fold Fins – very broad based

Paired Fins

Bony fishActinopterygii has ray fins, very flexible

with thin baseSacrcopterygii has fleshy muscular base

– Dipnoi has lobe fins– Crossopterygii has lobe fins that are called

fringe fins & have pterygiophores on one side of fin axis

Osteichthyes skeletonOsteichthyes skeleton

Pelvic finPectoral fin

Caudal fin

Dorsal fins

Anal fin

Origins of fins

From acanthodian spines?From fleshy folds?From gills?

Median fins – Dorsal and Anal fins

Dorsal and Anal Fins

Function for rolling, defense, displayLocation – rests on vertebral columnVariations among groups

Caudal fins

HeterocercalHypocercalDiphycercalHomocercal

– Teleosts– Neural and Hemal arch for support– Bony sheath for notochord

Pelvic finPectoral fin

Caudal fin

Dorsal fins

Anal fin

Fish tailsHeterocercal

HomocercalDiphycercal