74 MAMMALIAN ANATOMY 



edges of the emargination, bears a crescentic, smooth, cephalic artic- 

 ular surface which faces dorsally. The rest of the dorsal surface of 

 each lamina faces in its cephalic part dorsally and in its caudal part 

 dorsally, laterally, and toward the head. The ventral surface of the 

 laminae is concave from side to side. On the part which projects 

 beyond the dorsal surface of the body are the caudal articular 

 surfaces. These surfaces, also, are crescentic in outline and face 

 ventrally and slightly toward the tail. Owing to the curve in the 

 thoracic region of the vertebral column, the vertebrae caudal to the 

 third or fourth are tilted so that the dorsal surfaces face more toward 

 the head than when the bone is held with the ventral surface of the 

 body horizontal. 



The neural canal in the sixth thoracic vertebra is almost round. 



CHARACTERS OF THE REMAINING THORACIC VERTEBRAE. 



Nearly all the different vertebrae present individual characters 

 which enable them to he recognized, yet the fourth, fifth, sixth, and 

 seventh are so much alike that it is difficult to identify them in a col- 

 lection of vertebra? taken from different animals. If, however, these 

 four vertebrae are taken from one skeleton, they may be distinguished 

 by their relative size and by some minor characters. 



The following are the peculiarities of the individual thoracic 

 vertebrae : 



The First Thoracic Vertebra (Figs. 50, 51, 52). The distinguish- 

 ing characters of the first thoracic are the large and deeply cup-shaped 

 costal articular facet on the ventral surface of the transverse process, 

 and the entire facet on the cephalic end of the side of the body, for 

 articulation with the head of the first rib. 



The transverse process is prominent. It springs from the pedicle 

 low down ventrally and slopes laterally and ventrally. Owing to the 

 depth of the costal articular facet, the lateral surface of the process is 

 reduced to a thin, arcuate border. 



The cephalic and caudal articular processes are similar to the 

 processes on the cervical vertebrae, and are distinct outgrowths from 

 the arch. Each cephalic process appears to be a continuation toward 

 the head, and dorsally and laterally, of the cephalic half of the dorsal 

 end of the transverse process. Its articular surface faces equally 

 dorsally and medially. Each caudal articular process is situated at 



