THE OSTEOLOGY OF ELOTHEBltJM. 279 



like processes, such as are found in Oreodon and other White River ungulates. Between 

 these wings the hinder face of the hone is concave and at the bottom of this concavity are 

 two small, but profound pits. The supraoccipital is continued over upon the roof of the 

 cranium and forms a part of the sagittal crest. 



A considerable part of the periotic is exposed on the surface of the skull, at the bot- 

 tom of the lateral occipital fossa, where it is enclosed between the exoccipital and the 

 squamosal ; it does not give rise to any distinct mastoid process. 



The occiput of the European species, E. magnum, as figured by Kowalevsky ('76, 

 Taf. XVII, Fig. 5), is different in many details from that which characterizes the Amer- 

 ican species. It has more of an hour-glass shape, not so wide at the base, more contracted 

 in the middle and more expanded at the top, but with much less conspicuous wing-like 

 processes, and it has no such projection above the foramen magnum, nor such deep lateral 

 fossa?. The condyles are larger and of an entirely different shape, having their principal 

 diameter vertical, instead of transverse. The paroccipital processes are longer, more com- 

 pressed and not so widely extended laterally. The foramen magnum is large and of more 

 nearly circular outline. 



The basisphenoid is narrower than the basioccipital and is not keeled on the ventral 

 surface, but is otherwise like that bone. So much of its course is concealed by the union 

 of the palatines and pterygoids along the median line that its length cannot be deter- 

 mined, while the j)resphenoid is nowhere exposed to view T . 



The tympanic is very extensively developed (PI. XVIII, Fig. 1). Part of it is inflated 

 into an oval, somewhat flattened and rather small auditory bulla, which differs from that 

 of Hippopotamus and of all existing suillines in being hollow and not filled up with 

 spongy tissue. On the outer side of the bulla the tympanic is extended as a narrow strip, 

 which broadens considerably between the squamosal and the exoccipital, with both of 

 which it articulates suturally, as well as with the alisphenoid in front. The bulla itself 

 terminates anteriorly in a blunt spine. 



The alisphenoid is small and forms very little of the side of the cranium. It is must 

 elongate antero-posteriorly along the ventral line, but has hardly any distinctly deA'eloped 

 pterygoid process. At the line of the sphenoidal fissure, which notches but does not per- 

 forate the bone, the alisphenoid is narrowed, to expand again at its suture with the parie- 

 tal and frontal. The orbitosphenoid is relatively rather large, but is low in the vertical 

 dimension, and does not extend upward into the orbit proper. Tavo sharp ridges on the 

 external face of the bone enclose a V-shaped groove, in which lie the optic foramen and 

 foramen lacerum anterius. 



The parietals are very large proportionately to the size of the cranium, but quite 

 small as compared with the entire length of the skull ; they roof in most of the cerebral 



A. P. S. — VOE. XIX. 2 J. 



