THE OSTEOLOGY OF ELOTHERIUM. 291 
In Hippopotamus and in Sus this vertebra is very similar to that of Elotherium, but the 
neural spine is notably heavier. 
The fifth cervical vertebra las an even shorter neural arch than the fourth-and a 
much higher neural spine. ‘The spine tapers rapidly from the base upward and becomes 
very slender, but it is nearly straight and only slightly recurved. The neural canal 
is somewhat larger than in the fourth vertebra, but, as in all the cervicals, it is strikingly 
small as compared with the size of the vertebra as a whole. The diapophysis is strong 
and prominent, but more slender than on the preceding yertebra, while the inferior 
lamella, though relatively short from before backward, has attained great vertical height 
and is strongly everted. In Elotheriwm the fifth vertebra is of the same type as the sixth, 
whereas in Aippopotamus it more nearly resembles the fourth. 
The sixth cervical is very like the fifth, but displays certain obyious differences. 
Thus, the neural arch is even shorter antero-posteriorly, and the neural spine is higher, 
heavier and much more strongly recurved. The postzygapophyses are decidedly smaller 
and are very characteristic in their markedly oblique position, for they rise steeply back- 
ward in a way that occurs in none of the other yertebree. The diapophysis is shorter but 
heavier than that of the fifth, while the inferior lamella is of similar shape, but larger, 
higher and with the free margin more thickened. In Hippopotamus this vertebra has 
much the same construction as in Lotherium, but the spine is shorter and more massive 
and the inferior lamella is much larger. In Sus the sixth cervical bears considerable 
resemblance to that of the White River genus. 
The seventh cervical is characterized by the height and thickness of the spine, which 
in these respects much exceeds that of the sixth. This spine tapers superiorly, but 
expands again at the tip into a rough tubercle. The posterior zygapophyses stand at a 
higher level than the anterior pair and are unusually concave. The peculiarities seen in 
the postzygapophyses of the sixth and seyenth vertebree are to provide for the curvature 
of the neck, which changes its direction at this point. From the occiput to the sixth 
cervical the neck is nearly straight and inclines downward and backward, while the 
seventh vertebra begins the rise which culminates in the anterior thoracic region. This 
change in direction requires greater freedom of motion, which is supplied by the modifi- 
cation of the zygapophyses upon the vertebree mentioned. The transverse process is, as 
usual, not perforated by the vertebrarterial canal; it is rather short, but heavy and much 
expanded at the distal end. On the posterior face of the centrum are large facets for the 
heads of the first pair of ribs. In Hippopotamus the neural spine of the seventh cervical 
is relatively much longer and heavier than in Hlotheriwm or in Sus. 
As a whole, the neck of Hlotherium is short and massive, with very strongly 
developed processes for muscular and ligamentous attachments, as are indeed necessitated 
