6 4 



Field Columbia^ Museum— Geology, Vol. II. 



pophyses, to the sixteenth dorsal, scarcety differ in their shape and 

 relations to the centrum. These vertebrae may, therefore, be properly 

 called thoracic. From the seventeenth vertebra to the last one 

 preserved, the twenty-second post-cervical, the diapophyses decrease 

 rapidly in size, the last being scarcely more than half the length of 

 the fourth or fifth. In these posterior processes the proximal articu- 

 lation of the arch is as broad as in any of the others, but the distal 

 end of the process is more compressed, with only a small surface for 

 the small presacral ribs. Over the twentieth vertebra the matrix has 

 been cleared away sufficiently to disclose a posterior zygapophysis. 

 The free diapophysis in this vertebra is about fifty millimeters in 

 length, thirty in height, and about twenty in width. The posterior 

 zygapophysis arches upward and backward from the base of the free 

 process. 



MEASUREMENTS. 



LENGTH OF DIAPOPHYSES. 



First, 



Second, 



Third, 



47 mm. 

 65 « 



Fourth, . 



Fifth, 



Thirteenth, 



90 mm. 



95 " 



90 ** 



Eighteenth, 



Twentieth, 



Twenty-second, 



75 mm. 

 65 " 

 60 " 



