THE SKELETON OF THE TURTLE. THE VERTEBRAE. 219 



A. THE VERTEBRAL COLUMN AND RIBS. 



The number of vertebrae in the Green Turtle is thirty- 

 eight, not a great number as compared with that in many 

 reptiles, and of these eighteen are caudal. 



The vertebral column is divisible into four regions only 

 cervical, thoracic, sacral, and caudal. 



THE CERVICAL VERTEBRAE. 



These are eight in number, and are chiefly remarkable for 

 the great variety of articulating surfaces which their centra 

 present, and for their mobility upon one another. 



The first or atlas vertebra differs much from all the others 

 and consists of the following parts : 



a. the neural arch, formed of two separate ossifications 

 united in the mid-dorsal line ; 



b. the inferior arch ; 



c. the centrum, which is detached from the rest and 

 forms the odontoid process of the second vertebra. 



Each half of the neural arch consists of a ventral portion, 

 the pedicel, which lies more or less vertically and is united 

 ventrally to the inferior arch, and of a dorsal portion, the 

 lamina, which lies more or less horizontally and meets its 

 fellow in the middle line in front, partially roofing over the 

 neural canal. Each pedicel bears a facet on its anterior 

 surface, which, with a corresponding one on the inferior arch, 

 articulates with the occipital condyle of the skull. Three 

 similar facets occur also on the posterior surface of the 

 pedicel and inferior arch, and articulate with the odontoid 

 process. The laminae meet one another in front, but do not 

 fuse, while behind they are separated by a wide triangular 

 space. They bear a pair of small downwardly-directed facets, 

 the postzygapophyses, for articulation with the prezyga- 

 pophyses of the second vertebra. 



