278 THE OSTEOLOGY OF ELOTHERIUM. 
Il. Tue SKULL. 
The skull of Hlotherium is one of the most remarkable features of this very curious 
animal. It is characterized by great length and slenderness, with the supraoccipital and 
nasal bones lying in the same horizontal plane. The muzzle is exceedingly long and 
narrow, and tapers somewhat anteriorly, though expanded by the sockets of the great 
tusks; the orbit has been shifted far back, its anterior border being, in some species, over 
m 2, and in others above m 8. The cranium is short and of absurdly small capacity, 
which, with the great temporal openings, gives an almost reptilian appearance to the 
skull when viewed from above or below. The sagittal crest is very high and thin, and 
the zygomatic arches, though rather short, are enormously developed. One of the most 
peculiar features of the skull is the great, compressed plate which is given off from the 
ventral surface of the jugal and descends below the level of the lower jaw, and this gro- 
tesque appearance is further increased by two pairs of knob-like processes on the ventral 
borders of the mandible. The occiput (Pl. X VIII, Figs. 1,2) is high and very broad at - 
the base, but narrowing rapidly to the summit; above the foramen magnum it forms a 
broad, flat projection of almost uniform breadth, with a very deep fossa on each side of it. 
The basioccipital is stout and rather short, keeled in the median ventral line and 
slightly contracted to receive the auditory bulle ; at its junction with the basisphenoid it 
forms a pair of small, roughened tubercles. The exoccipitals are yery large bones, espe- 
cially in the transverse direction along the base of the occiput, dorsally they narrow fast. 
Above the foramen magnum they form the very broad, prominent and nearly square pro- 
jection which has already been mentioned ; this is thick and is filled with cancellous bone, 
the fossa for the vermis of the cerebellum making but a slight depression upon its internal 
face. On each side of the projection is a large and deep triangular fossa, which, how- 
ever, is not confined to the exoccipital, the periotic and squamosal both being concerned in 
its formation. The inferior part of the exoccipital extends widely outward, reaching to 
the line of the glenoid cavity, and ending in the large, prominent and massive, but not 
elongate paroccipital process. In this region the exoccipital is brought very close to the 
zygoma, but, ventrally at least, does not quite touch it, a narrow band of the tympanic inter- 
vening between them. The foramen magnum is strikingly small and of a transversely oval 
shape. The occipital condyles are relatively rather small, especially in the vertical dimen- 
sion, laterally they are well extended, and they are widely separated both aboye and below. 
In the very large /. imperator the external angles of the condyles are abruptly truncated 
in a curious way, and bear flat articular surfaces, though in some individuals this trunca- 
tion is found only on one side; while in the smaller species the condyles are of the usual 
form. The supraoccipital is a large bone, widest at the base (7. ¢., the suture with the 
exoccipitals) and narrowing dorsally. Superiorly it is drawn out into two posterior wing- 
