i8o 



CHORDATE ANATOMY 



The girdles of reptiles are essentially like those of amphibians. In the 

 turtle they become definitely Y-shaped. The clavicle fuses with the pre- 

 coracoid and becomes indistinguishable from it. The ilium connects with 



JO-PUBO-lSOflAWC CARTCLAGE- 



E. DACTYLETHRA 



a NECTURUS. 



Fig. 169. — A series of six appendicular skeletons illustrating the gradual emergence 

 of the elements of the pelvic girdle found in reptiles and mammals. They probably 

 represent fairly well stages in the evolution of the human pelvis. First came the separa- 

 tion of girdle and extremity (A and B) ; then the fusion of the paired elements of the 

 girdle into a median ventral cartilaginous plate (C and D) ; the differentiation of bony 

 ischium, pubis, and ischium (D and £); and finally the appearance of the obturator 

 foramen (F). There is no essential difference between the reptile and mammal girdle. 

 (Redrawn after Wilder, "History of the Human Body"; Henry Holt & Co.) 



SUPRASCAPULA| 

 SCAPULA' 



-OMOSTERNUM 



CLAVICLE^ 

 ACROMION- 



EPIPHYSIS 



OF CLAVICLEi INTER- 



\ .clavicular 



" 'ligament 



HUMERUS 

 ■'^PRECORACOID 



'HUMERUS 



-i--rnDarr,in COSTOCOR ACO I D/ 

 y-CORACOID LIGAMENT ^ 



--EPICORACOID CARTILAGES'^ 



LIGAMENT 



-STERNUM 



'sternum 



NSCAPULA 



/OSSA 

 SUPRASTERNALIA 



B 



Fig. 170. — Diagrams illustrating the fundamental similarity of the human (B) and 

 amphibian (A) pectoral girdle. In man the coracoid element has degenerated into a 

 process (coracoid) and a connective-tissue ligament containing occasional cartilage 

 nodules. (Redrawn after Huntington.) 



two sacral vertebrae. In pythons, a rudimentary hip girdle connects with 

 a pair of rudimentary claws in the anal region. Both are useless; both go 

 to prove the descent of serpents from tetrapod ancestors. 



