308 F. B. Loomis — Osteology and Affinities 



edges being slightly flexed downward. The anterior facet for 

 the atlas is a wide concave face extending in a trifle over half 

 a circle, and dying out on the neural arches. The odontoid 

 process is short and thick with a tubercle on its upper surface. 

 In this the genus differs from the early tylopods, which have a 

 semicylindrical odontoid, while that of the modern genera is 

 spout-like. The vertebrarterial canal is confluent with the 

 neural canal through the posterior third of the vertebra, then 

 enters the pedicle of the neural arch, passing obliquely through 

 and coming out about a third of the way from the front of the 

 centrum. Just in front of the vertebrarterial foramen there 

 is a wide opening for the exit of the second spinal nerve. 



The third, fourth and fifth cervicals are so similar that they 

 may be treated together. They are all long and slender, hav- 

 ing only the smallest vestiges of a spinous process, in which 

 feature they resemble the modern camels, even having the 

 characteristic to a more marked degree than any of the other 

 genera in the family. The transverse processes, expanding 

 wing-like on either side, extend the whole length of the cen- 

 trum, and then are prolonged into slender projections as seen 

 in fig. 12. These transverse processes do not have the anterior 

 portion of the wing prolonged into a distinct lobe, as is the 

 case in the modern Tylopoda ; but rather have the lobe barely 

 indicated, as is the case in Poebrotherium and Oxydactylus. 

 A ventral keel develops on the posterior third of the centrum, 

 expanding to the rear until it is very prominent. In none of 

 these three vertebrae is the vertebrarterial canal visible exter- 

 nally. On cervicals 3-7 the anterior of the centrum is moder- 

 ately convex, the posterior end concave. 



The sixth cervical is markedly different from the others. 



First its dorsal spine is vestigial, which is well developed in the 



modern camels and in Poebrotherium : then the transverse 



process is a short thin plate the distal end of which is bent 



backward. The interior lamellse are developed into wide 



F 12 plates which extend the whole length 



of the centrum and project downward. 



These are not, however, divided into 



an anterior and posterior lobes as in 



the modern tylopods, but have a 



straight lower border as is the case in 



Poebrotherium. The vertebrarterial 



canal enters the base of the neural 



Fig. 12. stenomyius pedicle at the rear and penetrates the 



hitchcocki, sixth cervical entire length, leaving just under the 



seen from the side, x 1/2. p reZ ygaphysis. 



The seventh cervical is much shorter than the others, and 

 has a moderate neural spine. The transverse processes are 



