180 ON THE EXTINCT MAMMALIA OF 



line with the basi-sphenoid. It is concave fore and aft, sti'aight and horizontal trans- 

 versely, and is nearly equal in diameter in those two directions. Its borders in front 

 and behind are prominent, and constitute ant- and post-glenoid tubercles. 



From the glenoid cavity the zygoma is directed forward, with a slight curvature 

 outward, and then inwardly to the face. The inner surface of the zygoma is directed 

 downward and outward, especially at its lower anterior portion. 



The posterior root of the zygoma inferiorly is exhibited in the form of a long, 

 transverse, strong and convex ridge, in a line with the spheno-occipital conjunction. 

 Posteriorly on the same line, but a little higher in position, is another long convex 

 ridge, less strong than the former, formed by the inferior border of the ex-occipital 

 extending to the par-occijiital. 



Between the two ridges just indicated is situated the tympanic bone. The inner 

 part of this forms a broad depressed convex bulla, but feebly developed compared 

 with its condition in the recent suilline animals, being proportionately smaller even 

 than in the Hippopotamus. The outer part of the tympanic bone forms a shelving 

 plate directed straight outward between the two ridges previously indicated, and 

 bounding inferiorly the auditory meatus. The direction of the latter and of its 

 external orifice is outward, with only a slight direction upwai'd and backward, and 

 the orifice is within the position of the paramastoid process. From the fore part of 

 the auditory capsule a strong conical eustachian process is directed downward and 

 forward. 



The foramen lacerum is a crescentoid space between the auditory bulla and the 

 basi- and ex-occipitals. The oval foramen is situated exterior to the root of the 

 pterygoid process, in front of the ali-sphenoid as it turns outwardly to contribute to 

 the fore part of the zygomatic root. 



The spheno-orbital foramen occupies the bottom of the orbital fossa, rather less 

 than an inch in advance of the oval foramina. About the fourth of an inch in front, 

 and internally to the position of the spheno-orbital, the optic foramen is situated. 



The stylal pit and the contiguous foramen appear to have their position just 

 external to the back part of the auditory capsule. - 



The middle palatine notch, like that of the extinct Chceropotamus, is much longer 

 than in recent suilline animals. It extends as far forward as the fore part of the 

 second true molars. It is somewhat ellipsoidal in form, and the included space is a 

 deep concave gutter continuous with the nasal cavities. 



The hard palate is long, and proportionately wider than in the Hog. It is 

 moderately arched both transversely and fore-and-aft. Its sides, as in living suilline 

 animals, are nearly parallel. 



The palatine plates of the palate bones are comparatively small, in consequence of 



