;^S ELEMENTS OF MAMMALIAN ANATOMY 



a small slit-like opening of the pterygoid (Vidian) canal for 

 the passage of a branch of the trigeminal nerve. The posterior 

 palatine foramina are small and are found about one-fourth 

 the distance forward from the caudal border of the hard palate. 

 The anterior palatine foramina or foramina incisiva are seen 

 just back of the incisor teeth. 



Viewed from the lateral aspect the skull, after the mandible 

 has been removed, is elongate with the ventral margin in its 

 general trend straight, but made emarginate by the presence 

 of several projections. The dorsal margin is somewhat flat- 

 tened in the middle but strongly curved at either end. The 

 surface is convex in both directions and is deeply impressed by 

 the orbital cavity and temporal fossa. The projections form- 

 ing the orbital rim and the zygomatic arches are prominent 

 features of the lateral view. The inner wall of the orbit pre- 

 sent a number of foramina. These are, beginning with the 

 most posterior: foramen ovale, foramen rotundum, the orbital 

 fissure, the optic foramen for the optic nerve, and the spheno- 

 palatine foramen. A slight depression limited dorsally by a 

 slightly curved elevated line joins the orbital fissure with the 

 sphenopalatine foramen. It makes the origin of the external 

 pterygoid muscle. Immediately in front of and slightly below 

 the sphenopalatine foramen is the much smaller posterior pala- 

 tine foramen. The infraorbital foramen pierces the maxillary at 

 the junction of the malar with the nasal process at the lower 

 anterior margin of the orbit. Above this is the nasolachrymal 

 groove and canal. The center of the orbital wall is perforated 

 by the ethnoidal foramen. A portion of the ethmoid is some- 

 times visible in the orbit as an irregular area, the os planum, 

 behind the lachrymal bone. 



Viewed from the frontal aspect the outline is nearly circular 

 when the mandible is present and somewhat greater than a 

 semicircle with it removed. The most striking feature from 

 this point of view are the four large openings in the bone frame- 

 work of the face: the orbits, the nasal aperture, and the oral 



