88 PATAGONIAN EXPEDITIONS I PALEONTOLOGY. 



processes are very slender and each is perforated by a vertebrarterial canal 

 so short as to be hardly more than a foramen. The neural canal is quite 

 large, especially the anterior opening ; the spine is so broken that its 

 shape cannot be accurately determined, but evidently it was a large, more 

 or less hatchet-shaped plate. The postzygapophyses are quite small. 



The (?) fifth cervical (Plate XII, fig. 5) has a short, broad, moderately 

 depressed and slightly opisthocoelous centrum ; the transverse process is 

 pierced in the normal way by the vertebrarterial canal, which is very much 

 longer than in the atlas or axis, and the inferior lamella, which is well 

 developed, is divided into anterior and posterior portions. The neural 

 canal is relatively large and the spine is distinct, though short and slender, 

 and inclined forward. The anterior zygapophyses are large and slightly 

 concave, the posterior much smaller. 



The only other cervical preserved is an uncharacteristic fragment of a 

 centrum, noteworthy only for the obliquity of the posterior face. 



In view of the great elongation of the limbs, the neck in Thoatherium 

 is surprisingly short, considerably shorter than the skull, to the basal 

 length of which it bears the proportion of 81 : 100, approximately. 



As already mentioned, the number of thoracic vertebrae is quite uncer- 

 tain, though the available evidence seems to indicate 15 as the more prob- 

 able number. On this assumption, the thoracic region, measured in a 

 straight line would stand in proportion to the skull as 160: 100. The 

 first thoracic vertebra has a small, somewhat depressed, trihedral centrum ; 

 the transverse process is short, but very broad and depressed, ending in a 

 very large deeply concave facet for the tubercle of the first rib : the neural 

 canal is large and the spine broad, heavy and, presumably, high, with 

 moderate backward inclination. In Diadiaphorus even the second thoracic 

 has a slender, tapering and relatively short spine, such as is found in the 

 posterior cervicals of many ungulates. The prezygapophyses are of 

 cervical type and the postzygapophyses quite like those of a lumbar 

 vertebra, small, convex and semicylindrical, projecting from the sides of 

 the neural arch : there are no metapophyses. 



The second thoracic has a slightly smaller centrum than the first and 

 considerably shorter and more rod-like transverse processes, which bear 

 much smaller and but slightly concave facets for the tubercles of the second 

 pair of ribs, while the neural canal and spine are similar to those of the 

 first ; the prezygapophyses are also similar, but smaller and less concave, 



