190 PATAGONIAN EXPEDITIONS: PAL/EONTOLOGY. 



neural arch and canal are low and wide and the spine is heavy and quite 

 prominent ; the zygapophyses, especially the anterior pair, are very large, 

 projecting in front of and behind the centrum, while the metapophyses 

 are low and rugose ; the transverse processes are long, broad and quite 

 thick. The second, third and fourth caudals resemble the first and their 

 centra are of nearly the same length, but grow narrower and thinner pos- 

 teriorly, while the facets for the chevron-bones are more prominent, en- 

 closing a deeper groove, and all the other processes are reduced. The 

 third vertebra closely resembles the anterior caudal of Nothrotherium 

 figured by Reinhardt ('78, Tab. II, figs. 4, 5). 



Next, after an interval, follows a group of four vertebrae, which may 

 be provisionally called the seventh, eighth, ninth and tenth. In these 

 the centra have become cylindrical and the chevron-facets are even more 

 prominent ; these facets are no longer continuous ridges, but are separated 

 by deep notches into anterior and posterior portions ; from the notch on 

 each side a well-defined groove passes up to the hinder border of the 

 transverse processes; the latter are short, but quite broad; the neural 

 canal is very small, especially on the ninth (?), which has no spine. 



Lastly, there is an isolated vertebra, probably the twelfth or thirteenth 

 caudal, in which the neural canal is hardly more than a pin-hole, the 

 chevron-facets are much less prominent and the grooves almost obsolete. 



The only chevron-bone preserved is that attached to the first and sec- 

 ond caudals; this is short and Y-shaped, broad antero-posteriorly and 

 thickened to form the vertebral facets ; the distal, undivided portion is 

 short and narrow, ending in a tubercle. 



MEASUREMENTS. 



Atlas, an tero -posterior length 031 Anterior thoracic, length of centrum. . . .023 



" width 078 " " width of anterior face .017 



" height, dorso-ventral 032 " " " " posterior face .020 



Axis, length of centrum 034 Anterior thoracic, width over transverse 



" width of anterior face 035 processes 067 



" " " posterior face 028 Anterior thoracic, height of neural spine 



Third cervical, length of centrum 024 above centrum 046 



" " width of anterior face . . .022 Anterior thoracic, width of neural spine 



" " " " posterior face . . .020 at tip 020 



Fourth cervical, length of centrum 025 First lumbar, length of centrum 032 



" " width of anterior face . .020 " " width of anterior face 037 



" " " " posterior face .019 



