170 



Comparative Morphology of Chordates 



Fig. 363. Skeleton of Sphenodon. (AT) Atlas; (AX) axis; (C) carpal bones; 

 (CL) clavicle; (CO) coracoid; (Dl, 2, 3, 4, 5) digits; (F) fibula; (FE) femur; 

 (HU) humerus; (HY) hyoid; (IL) ilium; (IS) ischium; (MC) metacarpals; (MT) 

 metatarsals; (PB) pubis; (PR) pro-atlas; (Q) quadrate; (R) radius; (SC) scapula: 

 (SP) spinal column (points to the spinous process of one of the thoracic vertebrae) : 

 (SSC) suprascapula; (T) tibia; (TA) tarsals; (U) ulna; (UP) uncinate process. 

 (After Headley. From Parker and Haswell: "Text-Book of Zoology." By permission 

 of The Macmillan Company, publishers.) 



sacral region, including, in modern reptiles, only two vertebrae; (4) 

 the postsacral, commonly called the "caudal," region, but inaccu- 

 rately so because its more anterior vertebrae lie within the hinder trunk 

 region of the body and not actually within the projecting tail. The 



Fig. 364. Three anterior vertebrae of 

 Rhamphosloma, a crocodilian (Schimke- 

 witsch). (a) atlas; (c) capitular head of rib; 

 (d) diapophysis; (ep) epistropheus; (o) 

 odontoid process; (p) parapophysis; (pa) 

 pro-atlas; (r 1 , r 2 , r 3 ) cervical ribs; (t.) tuber- 

 cular head of rib. The arrow is in the ver- 

 tebrarterial canal. (Courtesy. Kingsley: 

 " Comparative Anatomy of Vertebrates," 

 Philadelphia, The Blakiston Company.) 



numbers of vertebrae in the several regions are highly variable accord- 

 ing to the proportions of the body in different types of reptile. The 

 total number ranges from a minimum in short-bodied, short-tailed 

 turtles (usually 20 exclusive of the postsacrals) to nearly 400 in some 

 snakes. In snakes, legs being absent, no sacral region is recognizable 

 and there is no distinction between cervical and trunk regions. In the 

 alligator there are 9 cervical, 15 trunk, 2 sacral, and about 40 caudal 

 vertebrae. 



