THE VERTEBRAL COLUMN. 15 



The attached margin of each is about two-thirds the length of 

 the thinner free margin. The somewhat thicker caudal end 

 of the transverse process projects further caudad than any other 

 part of the vertebra and is separated by a slight notch from the 

 caudal articular facet. From the bottom of this notch the 

 foramen transversarium extends craniad and opens at the 

 middle of the ventral face of the transverse process. 



Epistropheus or Axis (Fig. 10, 2; Fig. 13). The second 

 cervical vertebra (epistropheus or axis) is not so wide as the 

 atlas but is much longer. Craniad the centrum is continued 

 into a slender conical, toothlike projec- 

 tion, the dens or odontoid process (Fig. 

 13, a) which represents the centrum of the 

 atlas. The dens is smooth below for 

 articulation with the ventral arch of the 

 atlas. It is rougher above. Laterad of " ' \r~~ 



the dens the centrum bears a pair of large FIG. 13. Axis OR EPIS- 

 cranial articular facets () which look TROPHEUS, SIDE VIEW. 



i .L j T-t. t. t- it. r <*' odontoid process or 



cramolaterad. Ihese have each the form dens; 6, cranial articular 



of a right-angled triangle with rounded facets; r, spinous process; 



83 d, caudal articular facet; 



angles, one side of the triangle being e , transverse process; /, 



nearly horizontal. Each is separated from foramen transversarium. 

 the" articular face of the dens by a roughened groove. The 

 spinous process (c] runs the length of the vertebral arch. It 

 extends craniad of the vertebral arch nearly as far as the dens, 

 as a flat rounded projection. Caudad of the vertebral arch it 

 projects for a short distance as a stout triangular spine. The 

 caudal articular facets (</) are borne on thickenings of the 

 caudolateral portions of the arch ; they face almost directly 

 ventrad. The transverse process (c] is slender and triangular 

 and directed nearly caudad. Its apex reaches no farther than 

 the caudal or articular face of the centrum. Its base is traversed 

 by the foramen transversarium (/). 



Differential Characters of the Cervical Vertebrae. It is 

 possible to identify each of the cervical vertebrae : 



The first by the absence of the centrum. 



The second by the dens or odontoid process. 



The third by the small spinous process and slightly marked 



