The Skeleton: Part 1, The Skull



In fish, amphibians, and reptiles, the jaw articulation invloves the articular bone of the lower jaw and the quadrate bone, which is usually attached to the cranium.



A transitional sequence in the positioning of the articular and quadrate from the jaw joint to the middle ear in mammals has been theorized. This concept is supported by the intermediate condition that has been observed in a number of synapsid fossils which are thought to link mammals to the synapsid reptilian lineage.


The absence of the articular and quadrate from the point of jaw articulation in mammals requires that the articulation point be between different skeletal elements, namely the mandible (dentary) and the temporal (squamosal).




















Divisions of the skull

Neurocranial division

Dermatocranial division

Splanchnocranial division

Sphenoid as a composite bone

Temporal as a composite bone

Occipital as a composite bone

Lamprey head skeleton

Shark and Ratfish head skeleton

Head skeleton of bony fishes

Neurocranial ossification in bony fishes

Dermal bones and scales in bony fishes

Dermal bones and the fish/amphibian link

Anapsids, diapsids, synapsids and others

Diapsids variations

Reduced dermal bone

Secondary palate formation

Hyomandibular expression

Quadrate and articular expression

Occipital condyle number

Sample Questions