286 THE OSTEOLOGY OE 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 very wide sigmoid notch. The mental foramen is 

 small, single, and placed below p Y - 



Several of the hyoid elements are preserved in connection with the skeleton of E. 

 ingens which forms the principal subject of this description. The stylohyal is quite long 

 and slender ; its proximal portion is laterally compressed and very 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 very thin and much compressed, but 

 broadened antero-posteriorly : the inferior part of the shaft is slender and oval in section, 

 with another cup-shaped expansion at the distal end. The epihyal and basihyal have 

 not been preserved. The thyrohyal is of remarkable length and slenderness, and obvi- 

 ously was not coossified 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 

 Hippopotamus, but are more slender and elongate. In the modern genus, on the other 

 hand, the thyrohyals arc very short, and arc ankylosed with the basihyal, a totally differ- 

 ent arrangement from that which characterizes Elotherium. 



From the foregoing description and accompanying figures it will be obvious that the 

 skull of. Elotherium is an extremely peculiar one. Among recent animals that of Hippo- 

 potamus approximates it must closely, and displays, with many striking differences, sev- 

 eral decided and. it may he, 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 very generally among the primitive ungulates of all groups. 

 Other similarities, again, are nut 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 genu- 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 Elotherium, 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. 



