THE OSTEOLOGY OF ELOTHERIUM. DATES) 
like processes, such as are found in Oveodon and other White River ungulates. Between 
these wings the hinder face of the bone is concaye 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 oceiput of the European species, Z. 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 
fosse. The condyles are larger and of an entirely different shape, haying 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 presphenoid is nowhere exposed to view. 
The tympanic is very extensively developed (Pl. X VIII, Fig. 1). Part of it is inflated 
into an oyal, 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 yery little of the side of the cranium. It is most 
elongate antero-posteriorly along the ventral line, but has hardly any distinctly developed 
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. Two sharp ridges on the 
external face of the bone enclose a V-shaped grooye, 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 
Ne By VO, WiIDK, DY A 
