450 AMPHIBIA. 



The first or mandibular arch gives origin inferiorly to Mecliel's 

 cartilage, which forms the basis and persistent core of the lower 

 jaw, and superiorly to the palato-pterygo-quadrate cartilage which 

 is represented in the adult by the minute quadrate bone, by the 

 suspensorial cartilage, and by other cartilages which are invested 

 by the pterygoid and palatine bones. 



The second or hyoid arch gives origin inferiorly to the hyoid plate, 

 superiorly, according to Parker, to the columella. 



Of four posterior branchial arches, there are in the adult persistent 

 remnants. 



The Limbs and Girdles. — The shoulder girdle consists of a 

 dorsal portion — the scapiila and the partially cartilaginous 

 supra-scapula, and of a ventral portion — the coracoid, and 

 the clavicle, and the cartilaginous precoracoid on which the 

 clavicle lies. There is some uncertainty, however, in regard 

 to the relations of the last two. The cavity or glenoid fossa 

 with which the upper-arm articulates, lies at the junction of 

 scapula and coracoid, and is bounded by them. 



Between the median ends of the coracoids lies a cartila- 

 ginous sternum ensheathed in bone, and prolonged poste- 

 riorly into a notched cartilaginous xiphisternum. Anterior to 

 the sternum is a bony portion called the omosternum, which 

 is prolonged forwards into an episternum cartilage. This 

 sternum does not arise like that of higher Vertebrates from 

 the ventral ends of ribs. Indeed, there are no ribs in the 

 frog, unless they be minute rudiments at the ends of the 

 tranverse processes. 



The skeleton of the fore-limb consists of an upper-arm or 

 humerus ; a fore-arm in which the inner radius and the 

 outer ulna are fused ; a wrist or carpus including two 

 proximal and three distal elements, and a central piece 

 wedged in between them ; five metacarpal bones, of which the 

 first — corresponding to the absent thumb— is very small; 

 and four fingers, of which the two innermost have two joints 

 or phalanges, while the two others have three. 



The pelvic girdle has a long V-shape, the ends of which 

 are cartilaginous and articulate with the expanded transverse 

 processes of the ninth or sacral vertebra. Each limb of the 

 V is an ilium ; the united posterior part consists of a fused 

 pair of ischia, and a ventral cartilaginous pubic portion. 

 Ilia, ischium, and pubes, unite in bounding the deep socket 

 or acetabulum with which the hind-leg articulates. 



