48 ELEMENTS OF MAMMALIAN ANATOMY 



muscles, and the first branch of the fifth nerve. This foramen 

 is between the aHsphcnoid and the orbitosphcnoid. The other 

 two foramina, rolundiim and ovale, transmit the second and 

 third divisions of the fifth nerve. 



The pterygoid portion of the sphenoid is a paired bone 

 (Figs. i8 and 19) lying on either side of the cranial half of 

 the basisphenoid and the caudal half of the presphenoid. 

 In the adult cat the sutures are sometimes obliterated so 

 that this bone appears as a caudal continuation of the pala- 

 tine. The two pterygoid bones or plates form the descend- 

 ing walls, and, together with the median portion of the sphenoid, 

 the roof of the median pterygoid fossa, whose cranial continua- 

 tion is the posterior nares. From the ventral 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 pterygoid processes is the small 

 external pterygoid fossa. 



The presphenoid hone is the narrow median bone extending 

 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. 17 and 18). 



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 maxillary although it 

 arises from a separate center of ossification. 



