328 VERTEBRATE ZOOLOGY 



floccular fossa ; the lower depression is the internal auditory mea- 

 tus, through which the auditory nerve enters the inner ear. Just 

 in front of it is the internal opening of the facial foramen. 



The nasal cavity occupies the anterior end of the skull. It is 

 divided into a right and a left cavity by the nasal septum, which 

 is formed by the vertical ethmoid cartilage, supported along its 

 ventral margin by the vertical bony vomer, its hinder wall being 

 formed by the cribriform plate of the same bone. The roof of 

 the nasal cavities is formed by the nasal bones, and their floor and 

 sides by the palatine, maxillaries, and intermaxillaries. The nasal 

 cavities communicate with the outside through the two nostrils, or 

 external nares, and with the pharynx through the internal nares, 

 or choanse, 'which are incompletely separated from each other. The 

 lateral and posterior walls of the nasal cavities are characterized 

 by intricately folded projections called the turbinals, or conchae, 

 which very much increase the extent of the inner surface. Three 

 series of these turbinals can be distinguished : the anterior maxillo- 

 turbinal, or inferior, concha ; the posterior and more dorsal ethmo- 

 turbinal, or superior, concha, projecting from the ethmoid bone; 

 and the middle concha, or nasoturbinal, projecting from the 

 nasal bone. 



Exercise 52. Draw a view of the section of the skull showing these 

 cavities and the boundaries of the bones. 



The lower jaw, or mandible, is a single bone which is composed 

 of a right and a left half joined in the middle line, and bears the 

 lower teeth. At the proximal end of each half are three prominent 

 processes: the condyloid process, which articulates with the gle- 

 noid cavity of the temporal bone ; the coronoid process, which is a 

 ridge with a deep groove just back of the teeth ; and the angular 

 process, which is the posterior end of the jaw. Near the anterior 

 end of the mandible, and just in front of the grinders, is the mental 

 foramen, through which the mandibular nerve, which innervates 

 the lower teeth, finds an exit. On the inner surface of the mandi- 

 ble, just behind the grinders, is the mandibular foramen, where this 

 nerve and the blood vessels of the jaw enter it. 

 Exercise 53. Draw a view of the lateral surface of the mandible. 



