7. The posterior nares are placed very far back, the nasal passages being as in mammals separated from the mouth by the long secondary palate.
8. There is a complicated system of Eustachian passages communicating at one end with the tympanic cavity and at the other end with the mouth cavity.
9. The interorbital septum is mainly cartilaginous, the presphenoidal and orbitosphenoidal regions remaining unossified.
The skull is divisible into three parts:—
(1) the cranium, (2) the lower jaw, (3) the hyoid.
The cranium may again for purposes of description be divided into:—
1. the cranium proper or brain case;
2. the bones connected with the several special sense organs;
3. the bones of the upper jaw, and suspensorial apparatus.
1. The Cranium proper or brain case.