VERTEBRAL COLUMN 87 



first vertebra to the vertebrae nearer the tail. Their length diminishes 

 from the first to the last. The cephalo-caudal diameter is least in the 

 second; in the first and third about equal, but beyond the third it 

 gradually increases to the tenth, inclusive. The lateral edges in the 

 first and second are nearly parallel with the median plane; in the 

 others, directed obliquely from the cephalic end laterally and toward 

 the tail. Cephalic and caudal tubercles begin to appear at the third 

 or fourth, and become on the tenth the rudiments of the mammillary 

 and accessory processes, which are well developed on the last three 

 vertebrae. 



Cephalic articular processes are distinct in the first, the second, 

 the eleventh, the twelfth, and the thirteenth. In these vertebrae the 

 cephalic articular surfaces face dorsally and medially ; in all the 

 others they face dorsally. 



The caudal articular processes are distinct on the first and on 

 the last four. The caudal articular surfaces on these vertebrae face 

 ventrally and laterally ; on all the rest they face ventrally. 



The distance from the ventral surface of the body to the caudal 

 edge of the caudal articular surface, measured on a line vertical to the 

 plane of the ventral surface of the body, is constant throughout the 

 series, but the distance between the edge of the articular surface and 

 the end of the spinous process becomes gradually less as we pass from 

 the cephalic vertebrae to those which are more caudal. This is clue 

 to an actual decrease in the length of the spinous processes, and also to 

 their increasing inclination toward the tail. 



The following table will aid in distinguishing the different thoracic 

 vertebrae ; the numbers refer to the vertebrae : 



TABLE. 



Transverse processes present, articulating with ribs. 



Cephalic articular processes distinct; project dorsally and 



laterally. 

 Caudal articular processes distinct: articular surfaces 



face also laterally 



Caudal articular processes not distinct ; articular surfaces 



face ventrally 



Cephalic articular processes not distinct from lamime. 



