BIO 342
Comparative Vertebrate Anatomy
Lecture Notes - Skeletal System II (Skull)

The Vertebrate Skull consists of: 

  1 - neurocranium (also called endocranium or primary braincase)

  2 - dermatocranium (membrane bones)

  3 - splanchnocranium (or visceral skeleton)


Cartilaginous fishes - retain a cartilaginous neurocranium (or chondrocranium) throughout life

Bony fishes, lungfishes, & most ganoids - retain highly cartilaginous neurocranium that is covered by membrane bone

Cyclostomes - the several cartilaginous components of the embryonic neurocranium remain in adults as more or less independent cartilages


Other bony vertebrates - embryonic cartilaginous neurocranium is largely replaced by replacement bone (the process of endochondral ossification occurs almost simultaneously at several ossification centers)

Neurocranial ossification centers: 

1 - occipital centers

2 - Sphenoid centers form:

3 - Ethmoid centers tend to remain cartilaginous & form

The ethmoid region is clearly visible within the bisected skull above. In most mammals, the nasal chamber
is large & filled with ridges from the ethmoid bones called the turbinals or ethmoturbinals. These bones are covered with
                  olfactory epithelium in life and serve to increase the surface area for olfaction (i.e., a more acute sense of smell).
                  Another ethmoid bone, the cribiform plate, separates the nasal chamber from the brain cavity within the skull.

4 - Otic centers - the cartilaginous otic capsule is replaced in lower vertebrates by several bones:

DERMATOCRANIUM - lies superficial to neurocranium & forms:

 Basic pattern of "roofing bones":

Bones of the upper jaw

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)

Opercular bones

Back to Skeletal System I

To Skeletal System III

Related links:

Skulls and jaws

Back to BIO 342 Syllabus