THE OSTEOLOGY OF ELOTHERIUM. 295 



other hand, increase in size and on the (?) fifth vertebra they curve toward each 

 other, almost meeting and enclosing a canal, which continues as far back as the (?) eighth 

 vertebra, behind which the hasmapophyses are again reduced. The middle portion of 

 the tail is composed of very long, cylindrical vertebra?, which in shape strikingly 

 resemble those of the great cats, and which are proportionately much longer, though 

 apparently less numerous than those of Anoplotherium. At the anterior end of each 

 vertebra are six prominent, nodular processes, the zygapophyses, transverse processes and 

 ha?mapophyses respectively. Posteriorly the centra become more and more slender, but 

 are not much diminished in length, for what appears to be the penultimate vertebra is 

 nearly as long as those in the middle region. The various processes are, however, 

 reduced to very insignificant proportions. The last vertebra has its anterior portion 

 shaped like that of its predecessor, but it rapidly tapers behind to a smooth, slender, 

 compressed and subcylindrical rod, with a club-shaped thickening at the end. As I have 

 seen but a single specimen of this curious vertebra, I cannot feel quite confident that its 

 shape is a normal one and not due to some injury or morbid process. 



The tail of Hippopotamus is of about the same relative length as that of Elothe- 

 rium, but the individual vertebrae are very different, being all shorter and heavier, and 

 diminishing in size more gradually to the end. In Sus the caudal vertebra? are somewhat 

 more like those of Elotherium, but none of them have such slender elongate centra. Little 

 is known concerning the caudals of Anthracotherium. Kowalevsky says of them: "Yon 

 den Schwanzwirbeln liegt mir nur ein einziges vor. Obwohl seine Erhaltung sehr 

 mangelhaft erscheint, kann man doch aus diesem kleinen Stuck den Schluss ziehen, dass 

 der Schwanz bei den Anthracotherieii kurz war und somit gar keine Aehnlicbkeit mit 

 dem sonderbar langen Schwanze der Anoplotherien hatte " ('73, p. 333 ; Taf. x, Fig. 36). 

 The vertebra described by Kowalevsky is an anterior caudal and is much smaller and in 

 every way more reduced than the corresponding ones of Elotherium. Among existing 

 artiodactyls, it is the giraffe which most resembles the White River genus in the peculiar 

 character of its caudal vertebra?. 



Measurements. 



Atlas, length 0.160 



Atlas, greatest width 570 



Axis, length of centrum .085 



Axis, 1 ength of odontoid 02(i 



Axis, anterior breadth 109 



Axis, posterior breadth 054 



Third cervical, length 066 



Seventh cervical, length 056 



First thoracic, length 051 



A. P. S. — VOL. XIX. 2 L. 



