286 THE OSTEOLOGY OF ELOTHERIUM. 
is strikingly low and small; it is of triangular shape, erect and not at all recurved, and 
is separated from the condyle by a yery wide sigmoid notch. The mental foramen is 
small, single, and placed below p 3. 
Several of the hyoid elements are preserved in connection with the skeleton of L. 
ingens which forms the principal subject of this description. The stylohyal is quite long 
and slender ; its proximal portion is laterally compressed and yery thin, but moderately 
broadened in the fore and aft direction. For the distal two-thirds of its length the bone 
is thicker and of a compressed oval section, expanding into a club-shaped thickening at 
the lower end, which is excavated for the connecting cartilage. The ceratohyal is con- 
siderably shorter than the stylohyal, but of quite similar shape; its proximal end bears 
a cup-shaped expansion, beneath which it becomes yery thin and much compressed, but 
broadened antero-posteriorly ; the inferior part of the shaft is slender and oyal in section, 
with another cup-shaped expansion at the distal end. The epihyal and basihyal haye 
not been preserved. The thyrohyal is of remarkable length and slenderness, and obyi- 
ously was not codssified with the basihyal; the bone is of subcylindrical shape, with 
expansions at the proximal and distal ends. 
This hyoid apparatus does not resemble that of any artiodactyl with which I have 
been able to compare it. The elements of the anterior arch somewhat resemble those of 
Fippopotamus, but are more slender and elongate. In the modern genus, on the other 
hand, the thyrohyals are very short, and are ankylosed with the basihyal, a totally differ- 
ent arrangement from that which characterizes Hlotherium. 
From the foregoing description and accompanying figures it will be obyious that the 
skull of Hlotherium is an extremely peculiar one. Among recent animals that of Hippo- 
potamus approximates it most closely, and displays, with many striking differences, sey- 
eral decided and, it may be, significant resemblances. Some of these resemblances, such 
as the straight cranio-facial axis and the long sagittal crest, are of no particular import- 
ance, because they occur so yery generally among the primitive ungulates of all groups. 
Other similarities, again, are not of this nature. The proportions of the cranial and 
facial regions, the degree of backward shifting of the orbits, the relations of the zygo- 
matic and paroccipital processes, the broadening of the muzzle, and the general plan of 
skull construction, are all similar in the two genera. On the other hand, each genus has 
certain peculiarities correlated with its manner of life. Thus, the elevation of the orbits 
and the backward displacement of the posterior nares in Hippopotamus are adaptations 
to its aquatic habits. Doubtless the extraordinary peculiarities of Hlotherium, such as 
the dependent processes of the jugals and the great knobs on the mandible, are of a sim- 
ilar nature, though, in the absence of the soft parts, it is difficult even to conjecture what 
their use may have been. 
