Skull Vertebrate Skull consists of Neurocranium Chondrocranium Dermatocranium

Skull Vertebrate Skull consists of : Neurocranium (Chondrocranium). Dermatocranium (membrane bones). Splanchnocranium (or visceral skeleton). Neurocranium : Protect the brain. Begin as cartilage that is partially or entirely replaced by bones )except in cartilaginous fishes. ( Neurocranium begins as pair of parachordal & & prechordal cartilages below the brain Neurocranium begins as pair of parachordal Parachordal cartilages expand & join; along with the notochord from the basal plate prechordal cartilages expand & join to form an ethmoid plate Cartilage appears in the : – olfactory capsule. – Otic capsule. Completion of floor, walls, & roof ethmoid plate ( fuses with olfactory capsules ) and basal plate (fuses with otic capsules(. Cartilaginous fishes : retain a cartilaginous throughout life. . Bony fishes, lungfishes, & most ganoids : cartilaginous neurocranium that is covered by membrane bone. Cyclostomes : cartilaginous neurocranium remain in adults. Other bony vertebrates : embryonic cartilaginous neurocranium is largely replaced by replacement bone.

Chondrocranium

Neurocranial ossification centers : Occipital centers : cartilage surrounding the foramen magnum may be replaced by as many as four bon – Basioccipital. – Exoccipital. – Supraocipital. Sphenoid centers form: basisphenoid bone (anterior to basioccipital) presphenoid bone side walls above basisphenoid & presphenoid form: – orbitosphenoid – pleurosphenoid – alisphenoid Ethmoid centers tend to remain cartilaginous & form: anterior to sphenoid. cribiform plate of ethmoid & several conchae (or ethmoturbinal bones). Otic centers: the cartilaginous otic capsule is replaced in lower vertebrates by several bones: prootic. opisthotic. epiotic.

DERMATOCRANIUM : lies superficial to neurocranium & forms : bones that form the roof of the brain & lateral walls of the skull bones of the upper jaw. bones of the palate. opercular bones. Bones of the upper jaw: Pterygoquadrate (palatoquadrate) cartilage) : ) cartilage premaxillae & maxillae make up the adult upper jaw. Bones of the lower jaw (mandible ): Mandible (the lower jaw) The mandible is the lower jaw. Mandible regions : The Body (corpus mandibulæ)- The body is curved like a horseshoe and has two surfaces and two borders. . The Ramus (ramus mandibulæ).

Palatal bones The floor on which the brain rests is at the same time the roof of the oral cavity in fishes & amphibians )primary palate ) Sharks : cartilaginous bony vertebrates : membrane bones form Birds, mammals, & some reptiles : a secondary ')false') palate develops creating a horizontal partition that separates the oral cavity into nasal & oral passages. The secondary palate is formed from processes of the premaxillae, and palatines.