448 Annals of the Carnegie Museum. 



hang in front but rises more abruptly, terminating above in the rugose 

 tubercle, or knob, which forms the summit of the sjjine. The anterior 

 opening of the vertebrarterial canal is placed well forward and has the 

 same lateral position as in the recent camel and the llama. The ex- 

 ternal opening is divided by a heavy bony plate, while that of the re- 

 cent forms is undivided. A tendency to divide in the recent genera, 

 especially in the llama, is sometimes shown by a short process on the 

 anterior border of the opening. The odontoid process has a less 

 spout-like appearance than in the llama, in this repect more nearly 

 resembling that of the recent camel. The transverse ])rocesses and 

 the inferior keel of the axis are proportionally lighter, and the latter 

 is less rugose but more produced than in the camel and the llama, 

 the expansion of the zygapophyses in O. loiigipes is not so great as in 

 recent forms. 



The length of the axis in comparison with that of the third cervical 

 is entirely different from that which obtains in any of the living forms. 

 In the recent camel the axis is the longest cervical. In the llama the 

 axis and the third cervical are of nearly equal length, while in O. 

 longipes the axis is much shorter than the third cervical. 



The Third Cervical. — llie third cervical vertebra is the longest in 

 the vertebral series. The neural spine is proportionally higher than 

 in the llama, but the laminae, extending from the spine to the post- 

 zygapophyses as seen in the llama, are wanting. The spine is lighter, 

 but higher, than in recent forms. The anterior and posterior divi- 

 sions of the transverse process are nearly as well developed and occupy 

 the same relative position as in the llama, /. c., the anterior process is 

 placed somewhat lower down on the centrum and is directed outward, 

 downward, and forward, while the posterior process is situated higher 

 on the centrum and is more nearly horizontal. The inferior keel is a 

 prominent rugose tubercle and extends more downward, but is not so 

 heavy as that of the llama. In the type, the keel does not extend so 

 far forward as in the llama, while other individuals of the same genus 

 show a faintly marked keel throughout the entire length of the centrum. 

 The pedicles are deeply notched, especially anteriorly, to admit the 

 passage of the spinal nerves. On this vertebra, there is no visible 

 vertebrarterial canal. From the base of the prezygapophysis there is 

 a sharp ridge extending posteriorly along the pedicle for some distance, 

 which is similar to that in PocbrofJieriuin and the recent forms. The 

 postzygapophyses are heavier than the prezygapophyses and more 

 expanded laterally. 



