BY W. J. McKAY. 917 



The Vertebral Column. 



The vertebral column of ophidians is generally divided into two 

 regions, a costal and a caudal. Rochebriine has, however, gone 

 very fully into the subject of the vertebrae of snakes, and he 

 distinguishes five regions, cervical, thoracic, pelvic, sacral, and 

 coccygeal or caudal. 



The cervical vertebriB are two in number, and are devoid of ribs ; 

 they represent the atlas and axis. The thoracic and pelvic vertebrae 

 have ribs, with ossified processes anchylosed to their lateral 

 aspects. The caudal are distinguished by possessing a bifid hypa- 

 pophysis. The only difficulty that arises is in distinguishing the 

 thoracic vertebrae from the pelvic. The thoracic possess hypa- 

 pophyses without exception ; the pelvic in certain forms only. 

 When, therefore, both regions have hypapophyses Rochebrune 

 distinguishes between them thus : — 



" Thoracic. — Brievete relative du corps, surelevation et incli- 

 naison des lames, abaissement brusque et raccourcissement des 

 processus, direction oblique du tenon, position elevee des tuber- 

 cules costaux ; developpement exagere des apophyses epineuses 

 superieures et inferieures ; largeur de la partie superieure du trou 

 rachidien." 



^^ Pelvic. — Epaisseur et longueur relative du corps; aplatisse- 

 ment et ecartement des lames ; amincissement et relevement de 

 I'extremite des processus ; direction droite du tenon ; position en 

 dessous des tubercules costaux ; developpement des apophyses 

 transverses ; brievete et largeur relatives de I'apophyse epineuse ; 

 brievete et inclinaison de I'hypapophyse ; aplatissement de la 

 partie superieure du trou rachidien." 



Taking a thoracic vertebra we shall compare the vertebrae of the 

 other regions with it. 



Centrum : The centra are procoelous. The articular faces are 

 ellipsoidal, the long axis being transverse. The edge of the 

 " socket " is slightly concave above and below, the appearance 



