48 PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 



The transverse process is very large, though somewhat smaller than that 

 of the first, and its dorsal border is upturned, as if to form an incipient 

 metapophysis. The zygapophyses are adapted to the very oblique posi- 

 tion of the vertebra, the anterior pair being placed at a much lower level 

 than the posterior, and this same obliquity makes the end of the spine 

 rise a little higher than that of the first, though the spine itself is slightly 

 shorter, less tapering and of a more uniform width. 



The succeeding thoracic vertebrae have smaller centra, which are short, 

 broad, depressed and opisthoccelous ; they increase in size posteriorly, so 

 that in the hinder part of the region they are almost as large as the lum- 

 bars. The obliquity of position continues as far as the fifth vertebra, 

 which marks the summit of the arch, its spine rising higher than any of 

 the others. The neural spines became successively shorter and, as far 

 back as the sixth thoracic, are increasingly oblique in direction. While 

 the spines of the first two vertebrae are parallel, from the second to the 

 sixth they are very divergent, radiating almost like the sticks of a fan, 

 though less regularly. This arrangement of the spines is such as to sug- 

 gest a distinct hump at the shoulders, for there is a sudden descent from 

 the sixth to the seventh, and the lowest point in the upper line of the 

 back is at the tenth thoracic, behind which the line rises slightly to the 

 sacrum. In modern genera the line connecting the ends of the neural 

 spines is a gentle and nearly uniform curve ; except in Priodorites, in 

 which it is somewhat irregular. 



In the hinder part of the thoracic region the spines are shorter, much 

 broader and heavier than in the forward part. The transverse processes 

 grow smaller posteriorly and are not conspicuous behind the sixth ver- 

 tebra ; their place is taken by the metapophyses, which begin to be prom- 

 inent on the seventh, growing larger on each successive vertebra, and are 

 extremely long and heavy, almost as much so as in Priodontes, and rise 

 more steeply than in that genus. The accessory articular processes do 

 not differ in any significant way from those of Stcgotherium. 



The three lumbar vertebrae have short and depressed, but broad and 

 heavy centra, with ventral ridges, which are most prominent on the 

 second ; the transverse processes are very short, curving forward and 

 downward and ending in bluntly rounded points ; the metapophyses are 

 extremely long and heavy, rising steeply upward and outward and 

 slightly forward, and ending in club-shaped tips for the support of the 



