170 ANATOMICAL TBCSNOLOGT. 



axial support of the tail ; and cephalad it is articulated diarthro- 

 dially with the occipital region of the skull. ' ' The different verte- 

 brae, with some exceptions (§ 458), remain through life distinct from 

 each other, though closely connected by means of fibrous struc- 

 tures which permit a certain but limited amount of motion between 

 them." 



§ 462. "Although the vertebrse of different regions present 

 great diversities of form, there is a certain general resemblance 

 among them showing a common plan of structure. This plan is, 

 however, worked out variously in different regions by change of 

 form and the suppression or superaddition of parts, thus fitting 

 them to fulfill their special purpose." — Flower, A, 10. 



In general, each vertebra is composed of a solid subcylindrical 

 centrum or body, and a bony arch (neural arch), with various 

 processes, extending dorsad therefrom (Fig. 52-55). 



§ 463. Regions of the Vertebrsd Column. — For convenience of 

 description, the whole vertebral column has been divided into five 

 regions, named in order from the head : — Cervical (7) ; Thoracic or 

 Dorsal (13) ; Lumbar (7) ; Sacral (3) ; Caudal or Tail (22), (Fig. 30). 



The middle Cervical, Thoracic and Lumbar vertebrae are shown 

 in Fig. 53-55, where the special characters of these three groups are 

 well illustrated. 



§ 464. Distinguishing the Five Groups of Vertebrae and the 

 Ends of the First Four Groups. — The cermcal vertebrae, except the 

 7th, are distinguished by the presence in the diapophysis of the 

 vertehr arterial foramen (§ 473). 



The 7th cervical is distinguished from the thoracics by the ab- 

 sence from its prominent diapophysis of an Arthron tuberculi, and 

 by the absence of an Arthron capitelli from the cephalic end of the 

 centrum (Fig. 52). It differs from the other groups by its short 

 wide centrum, large neural foramen and slender neural spine. 



The thoracic vertebrse differ from all the others by the presence 

 of an Arthron capitelli on the cephalic end of the centrum or upon 

 both ends. 



The lumbar vertebrse may be distinguished by their long sub- 

 cylindrical centra, and by the cephalic inclination of the neura- 

 pophyses and of all the diapophyses except the first. 



The sacral vertebrse are more or less completely anchylosed. 



The caudal vertebrse differ from the others by the smallness or 



