28 SCOTT. [Vol. V. 



der than in the existing tylopodans, and so far as can be judged 

 from the specimens at hand were also proportionately longer. 

 Metapophyses first appear on the ninth vertebra, rising from the 

 transverse process just above the facet for the tubercle of the 

 rib ; they increase in size on the tenth and eleventh, but retain- 

 ing the same position, while on the twelfth and thirteenth they 

 shift to the prezygapophyses. The centra of the posterior dor- 

 sals become elongated, broad, and depressed, and have nearly 

 flat faces. The spines are strongly inclined backward until the 

 twelfth vertebra is reached, which is the anticlinal, and has a 

 curious plate-like spine, with deeply concave anterior and nearly 

 straight and vertical posterior margin. The last dorsal has a 

 broad, plate-like spine, like that of a lumbar vertebra. On the 

 eleventh vertebra the postzygapophyses tend to become cylin- 

 drical, and are received into the concave prezygapophyses of the 

 twelfth, on which vertebra and the thirteenth these processes 

 are of the interlocking cylindrical type common to all artiodac- 

 tyls. The spinal nerves pass out between the neural arches, 

 and in no case are the pedicles perforated by then. The chief 

 difference between the dorsal vertebrae of Pcebrotherium and 

 those of the recent Tylopoda lies in the character of the spines, 

 which in the latter^ and more especially in the camel, are ex- 

 tremely massive, while in the Miocene genus they are very 

 slender. 



The lumbar vertebra probably number six, or perhaps seven, 

 and are relatively large. The centra are long, broad, and de- 

 pressed, and become more so as we pass backward : they have 

 nearly flat or slightly opisthocoelous faces, and are keeled infe- 

 riorly ; while in the posterior part of the region there is a faintly 

 marked ridge on each side of this keel. Both the neural spines 

 and the transverse processes are, unfortunately, broken away in 

 all the specimens which I have seen ; but from the fractured 

 surfaces, it is clear that the latter had a greater antero-posterior 

 extent than in the recent genera, and that the neural spines 

 were more compressed and decidedly less massive. The zyga- 

 pophyses are of the typical interlocking shape, but they differ 

 in detail from the structure seen in the modern genera. In the 

 camel an additional complication has arisen, in the appearance 

 of a concave surface above the postzygapophyses, the episphe- 

 nial process, which also occurs in several of the true ruminants. 



