702 



Co M I' A R A T I V E ANATOMY 



size and usurps the function of the clavicle, while the clavicles themselves 

 disappear. 



Other bones from the skin may develop, such as the supracleithra 

 (post-temporals or supra-temporals). These connect the girdle with the 

 skull ; sometimes also post-clavicles and infra-clavicles develop. 



A review of the 

 appendicular skeleton, 

 as formed embryolog- 

 ically in the chick and 

 frog, will give one a 

 good idea of the parts 

 as they appear in am- 

 phibia. In the reptiles, 

 there is a considerable 

 variation in the shoul- 

 der girdle. In the 

 turtle, its position in- 

 side the carapace and 

 internal to the ribs is 

 supposed to be due to 

 the fact that the girdle 

 begins its development 

 in front of the ribs, and 

 later sinks to the posi- 

 tion it is to occupy in 

 adult life. The scap- 

 ula, procoracoid, and 

 Fig - 417 - coracoid, are well de- 



Tortoise skeleton Cistudo lutaria. Ventral side with plas- velopcd. The median 

 tron removed and placed at one side. C, costal plate ; Co, cora- 

 coid ; e, endoplastron ; ep, epiplastron (clavicle) ; F, fibula; Fe, ends OI the latter are 

 femur ; H, humerus ; Hyp, hyoplastron ; Hpp, hypoplastron ; II, , 



ilium ; Js, ischium ; M, marginal plates ; Nu, nuchal plates ; Py, Connected by a Cartlla- 

 pygal plates; R, radius; sc, scapula; T, tibia; U, ulna; Xp, crinmtc GrMV/~vf i/-'^1 T,-. 

 xiphiplastron. (From Parker and Haswell after Zittel). gttlOUS eplCOraCOld. Ill 



t>, erf. 



