256 



VERTEBRATES. 



tals, two long, narrow nasals complete the median dorsal 

 surface, and form the bony support of the snout. The 

 two stout bones which carry the upper incisors, and 

 which are situated beneath the nasals, and meet on the 

 median line in front, are the premaxillaries. Behind 

 them are the maxillaries, large and irregular, forming 

 the greater part of the skeleton of the upper jaw. Ven- 

 trally they bear the upper molars ; and each sends out a 

 stout lateral process, which forms part of the anterior 



boundary of the orbit. 

 The nasal cavity 

 lies beneath the na- 

 sals and above the 

 maxillaries and pre- 

 maxillaries. Looking 

 into it from the front, 

 a number of thin, 

 irregular plates of 

 bone (the turbinals) 

 will be seen. The 

 anterior of these, the 

 more delicate and 



SKULL OF RABBIT (dorsal and ventral views of comp l ex j n structure, 

 cranium). 



are developed from 



the maxillaries, and are called the maxillo-turbinals. The 

 posterior are developed from the (concealed) ethmoid, 

 and are called ethmoturbinals. The ethmoid terminates 

 posteriorly in a transverse cribriform plate, set in the an- 

 terior end of the cranial cavity. This plate may be seen 

 in a skull from which the roof of the cranial cavity has 

 been removed. It is perforated for the passage of the 

 branches of the olfactory nerves to the nose. Within 

 the nasal cavity, the terminations of these nerves are dis- 

 tributed through the mucous membrane, which covers the 

 turbinal bones. The great extent of surface over which 



