THE OSTEOLOGY OF ELOTHEEITJM. 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 has 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 vertebra, while the inferior 

 lamella, though relatively short from before backward, has attained great vertical height 

 and is strongly everted. In Elotherium the fifth vertebra is of the same type as the sixth, 

 whereas in Hippopotamus it more nearly resembles the fourth. 



The sixth cervical is very like the fifth, but displays certain obvious 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 jwsition, for they rise steeply back- 

 ward in a way that occurs in none of the other vertebrae. 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 Elotherium, but the spine is shorter and more massive 

 and the inferior lamella is much larger. In Sits 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 seventh vertebrae 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 vertebra? mentioned. The transverse jn-ocess 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 Elotherium or in Sus. 



As a whole, the neck of Elotherium is short and massive, with very strongly 

 developed processes for muscular and ligamentous attachments, as are indeed necessitated 



