3 i6 COMPARATIVE ZOOLOGY OF CHORD ATES 



Amphibian of the Carboniferous period), the clavicular pectoral 

 girdle is represented by the clavicle, cleithrum, supra-cleithrum 

 and post- temporal, which latter is attached to the hind end of 

 the skull, just as in bony fish. To these is added a median 

 ventral interclavicle. As in all Tetrapods, the scapula (cartilage- 

 bone of scapular girdle) rests on, but is not attached to, the 

 ribs. The pelvic girdle of Eogyrinus is interesting in that the 

 ilium rests on the ribs without fusing with them to form a 

 sacrum. In this respect, the pectoral and pelvic girdles are 

 similar, but in higher forms the ilium becomes firmly attached 



Fig. 161. — Ventral view of the pectoral girdle of Ornithorhynchus. 

 ec, epicoracoid (or precoracoid). Other letters as Fig. 160. 



to one or more sacral vertebrae. In addition to the ilium, 

 the pelvic girdle contains the pubis and ischium. 



In the earliest land- vertebrates, the function of the limbs 

 was not to support the body of the animal but to row it along 

 while its ventral surface rested on the ground. Such move- 

 ment must have been slow, and improvement came in the 

 reptiles, in which the limbs lift the body off the ground. In 

 them, there was no friction to be overcome between the body 

 and the ground, and the higher the body was lifted, the longer 

 the limbs, the longer the stride and the faster was the pace. 

 In the reptiles the clavicular pectoral girdle is reduced to the 

 clavicle and interclavicle (the cleithrum persists only in some 

 primitive forms), while the scapular girdle usually consists 



