Skeletal System: Skull

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Cranial Skeleton is of three parts:

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CRANIAL SKELETON

Chondrocranium

Splanchnocranium

Dermatocranium

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BLUE- Chondrocranium YELLOW- Splanchnocranium PINK- Dermatocranium

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-elements found at the back of the vertebrae

Nineteenth century morphologists propose that the vertebral column is the ancient ancestors of the chondrocranium.

-neural crest cells and mesenchyme cells differentiate to form chondrocranium

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cos 𝛼 + cos 𝛽 = 2 cos1

2𝛼 + 𝛽 cos

1

2𝛼 − 𝛽

Vhi Ann J Bajardo

Vhi Ann J Bajardo

neural crest cells contributions to the skull

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-elements contribute to filter-feeding surfaces (Amphioxus), jaws and hyoid apparatus (Gnathostomes)

-neural crest cells arise to form splanchnocranium

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BLUE- Chondrocranium YELLOW- Splanchnocranium PINK- Dermatocranium

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THE PARTS OF CRANIAL SKELETON shown in FIGURE 7.1

Derivatives of Neural Crest Cells

Protochordates NCC migrate to the body wall

from the neural tube

NCC differentiates into pigment cells

Vertebrates

NCC moves into the walls of pharynx

NCC differentiates into jaws and gill arches

Vhi Ann J Bajardo

Vhi Ann J Bajardo

a. ORIGIN OF JAWS

-an anterior pair of gill arches gave rise to jaws

-branchial arch musculature were transformed and modified into musculature of the jaws

Divisions of mandibular arch of jawless fishes:

Neurocranium (dorsal)

Mandible (ventral)

Vhi Ann J Bajardo

Vhi Ann J Bajardo

Embryology of Pharyngeal Arches

Protochordates

Pharyngeal arches rises from the mesoderm

Most Vertebrates

Pharyngeal arches rises from neural crest cells

Vhi Ann J Bajardo

Vhi Ann J Bajardo

b. TYPES OF JAW ATTACHMENTS

The points at which the jaws attach to the rest of the skull defines the type of jaw attachment

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Jaw Attachment How Jaws are Attached Vertebrates

Paleostyly no arches attach to the skull agnathans

Euautostylymandibular arch suspended from

the skullacanthodians,

placoderms

Amphistylyjaws attached through ligament

and hyomandibula

extinct sharks, rhipistians,

osteichthyans

Hyostylymandibular arch attached through

hyomandibulamodern bony fishes,

extant sharks

Metautostylyjaws attached directly to braincase

through quadrateamphibians, reptiles,

birds

Craniostylyupper jaw incorporated to the

braincase; lower jaw suspended through dermal squamosal bone

mammals

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Vhi Ann J Bajardo

-consists of dermal bones contributing the skull

-forms sides and roof of the skull

-mesenchymal and ectomesenchymal tissues of the dermis

Vhi Ann J Bajardo

Vhi Ann J Bajardo

Vhi Ann J Bajardo

Braincase-

Jaws-

Hyoid Apparatus- supports the tongue and the floor of the mouth

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OVERVIEW

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-movement between the upper jaw and the braincase about joints between them Cranial kinesis: movement between the upper jaw and braincase

advantages: provides a way to change the size and configuration of the

mouth rapidly optimize biting and rapid feeding.

disadvantages: lose force, difficult to optimize apposition of occlusive surfaces.

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CRANIAL KINESIS

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Vhi Ann J Bajardo