3 6 ELEMENTS OF MAMMALIAN ANATOMY. 



sphenoid, the roof of the median pterygoid fossa, whose 

 cranial continuation is the posterior nares. From the ven- 

 tral posterior angle of each projects the hamular process, 

 dorsal of which is seen the small external pterygoid process. 

 Between the bases of the hamular and the external ptery- 

 goid processes is the small external pterygoid fossa. 



The presphenoid bone is the narrow median bone extend- 

 ing from the basisphenoid to the vomer. It contains within 

 it two large sinuses into which project the ventral scrolls 

 of the ethmoturbinal bones. The orbitosphenoids enter 

 into the formation of the medial walls of the orbits and are 

 perforated at their bases by the optic foramina, through 

 which pass the optic nerves. 



BONES OF THE FACE. 



There are seven paired bones in the face and two single 

 ones, making in all sixteen (Figs. 16 and 17). 



The premaxillary, with its fellow, extends ventrad and 

 laterad of the anterior nares. These bones bear the six 

 incisor teeth. The anterior palatine or incisor foramina 

 connect the oral cavity with that of the anterior nares. In 

 life, these foramina transmit the naso-palatine nerves. In 

 the Primates, the premaxillary is anchylosed to the maxil- 

 lary although it arises from a separate center of ossification. 



The maxillary is a paired bone which meets its fellow 

 in the median line in the roof of the mouth. All its articu- 

 lations are visible externally except those with the maxillo- 

 turbinal, ethmoid, and vomer. Five teeth, a canine, three 

 premolars, and a molar, are present in this bone of the 

 adult cat. The molar is wanting to the young. The several 

 portions of the bone are as follows: the palatine plate, 

 appearing in the roof of the mouth; the nasal process, ex- 

 tending dorso-caudad to the frontal ; the malar process, ex- 

 tending ventrad to the orbit to articulate with the malar 



