35^ SMITHSONIAN MISCELLANEOUS COLLECTIONS [vOL. 45 



VERTEBRAL COLUMN 

 Leporid.e 



The vertebral column in the different members of the Leporidae, 

 while of the same general type throughout, presents several peculiar- 

 ities, constant for the various genera. The vertebral column in the 

 Ochotonidffi, on the other hand, is different in many ways from 

 that of the Leporid^e, as will be detailed below. The different sec- 

 tions of the vertebral column will be taken up successively, begin- 

 ning with a general account of the structures of each series, fol- 

 lowed by a discussion of the variations each series presents in the 

 various genera. 



Cervical Vcrtchrcc (pi. xcii, 2-10). — The first cervical or atlas is 

 large, with conspicuous wing-like transverse processes. 



The second cervical or axis has a well-developed cylindric odontoid 

 process. Its centrum is long, its neural spine well developed, the 

 antero-posterior length of the neural spine being greater than the 

 corresponding length of the centrum. Transverse processes are 

 present as caudad projecting spines on each side. 



The third, fourth, and fifth cervical vertebra have practically no 

 neural spines ; on the sixth there is a small neural spine and on the 

 seventh a larger one. 



The third, fourth, and fifth have spine-like transverse processes 

 directed backward. The sixth and seventh have well-developed 

 transverse processes, not so spine-like as they are in the third, fourth, 

 and fifth, and they project outward. 



In the fourth, fifth, and sixth, the costal process is well developed 

 as an expanded plate projecting laterally from the centrum and ex- 

 tending farther both cephalad and caudad than the centrum to which 

 it is attached. With the true transverse process, this plate encloses 

 the vertebral foramen. This plate-like expansion is largest in the 

 sixth cervical, steadily decreases in size in each further cephalad 

 vertebra, is merely indicated in the third cervical, and in the axis is 

 seen only as the ventral wall of the vertebral foramen. 



The seventh cervical is very similar to the first dorsal, differing 

 from it in that it has on each side a vertebral foramen and no facets 

 for the articulation of ribs. 



The articulating surfaces of the centra are oblicjue, sloping from 

 above downward and backward. 



The laminae of the axis, of the third, and of the fourth are well 

 developed, forming a complete roof for the spinal canal. The 

 laminae of the fifth are less extensively developed, and of the sixth 



