PkIKRSOX : OsiKOLOGV OI OXVDACIVLUS. 449 



Fourth Cervical. — The fourth cervical is essentially a duplication 

 of the third, except that it is heavier. The spine differs from that in 

 recent forms by being broader antero-posteriorly. It extends unin- 

 terruptedly backwards to the base of the postzygapophyses. The infe- 

 rior keel is heavy and terminates in a rugose knob at the ])Osterior 

 inferior end of the centrum. There is no vertebrarterial canal. 



The Fifth Cervical. — The fifth cervical is about 20 mm. shorter 

 than the fourth, but heavier than that vertebra. The neural spine 

 more nearly resembles that of the same vertebra in recent forms being 

 somewhat depressed posteriorly and broad superiorly. The anterior 

 division of the transverse {)rocess is directed downward and forward 

 extending somewhat in advance of the centrum, similar to that of the 

 llama. The inferior keel is as prominent as that of the fourth cervi- 

 cal. The other characters are similar to those of the latter vertel)ra. 



Sixth Cervical. — The sixth cervical is proportionally shorter than 

 is that in the llama and retains the characters seen in that oi Fo'ehro- 

 theriuin. The corresponding vertebra in the recent camel is remark- 

 ably similar in character while that of the llama is widely different. 

 In Oxydactyliis the centrum is 39 mm. shorter than that of the fifth, 

 more strongly convex anteriorly, and somewhat more concave posteri- 

 orly than any of the preceding vertebrae. The inferior keel is well 

 represented. The neural spine is high, similar to that of the camel 

 and occupies the entire length of the superior border of the neural 

 arch. In the llama the spine is represented by a low heavy ridge 

 which is confluent with the postzygapophyses, while in Oxydactyliis 

 longipes and the recent camel the spine is entirely independent and 

 extends to the posterior margin of the neural arch. The transverse 

 process is like that of the llama, a thin plate of bone occupying a con- 

 siderable portion of the side of the centrum. The inferior lamella, as 

 in Po'ehrotheriiun '" and Cameliis bactrianiis, is not divided, while in the 

 llama there is a distinct posterior and anterior division of this element. 

 In the type, this lamella occupies the entire length of the inferior and 

 exterior part of the centrum, pointing downward and outward ; the 

 anterior and posterior terminations are rounded tubercles connected 

 by a thin and slightly emarginated plate of bone. The vertebrarterial 

 canal is located in the pedicle as is that in the llama. 



The Seventh Cervical. — The seventh cervical is approximately 30 

 mm. shorter than the sixth. The anterior face of the centrum is de- 



^^Journ. Morp/i., Vol. V, No. i, p. 26. 



