536 AMPHIBIA. 



dorsal portion — the scapula and the partially cartilaginous 

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

 the pre-coracoid. With the latter, according to some 

 authorities, a thin clavicle is associated. The glenoid cavity, 

 with which the humerus articulates, is formed by the junction 

 of scapula and coracoid. 



Between the median ends of the coracoids lie two fused 

 cartilaginous epicoracoids, behind which is a bony part of 

 the sternum, prolonged posteriorly into a notched cartila- 

 ginous xiphisternum. Anteriorly lies a bony portion called 

 the omosternum, which is prolonged forwards into an epi- 

 sternum cartilage. This sternum does not arise like that of 

 higher Vertebrates, from a fusion of the ventral ends of ribs. 

 Indeed, there are no ribs in the frog, unless they be minute 

 rudiments at the ends of the transverse processes. 



The true frogs ( Ranidje) have what is called a firmistemal pectoral 

 arch, in which precoracoid and coracoid nearly abut on the middle line, 

 and are only narrowly separated by the epicoracoids. In toads, tree-frogs, 

 etc., the arch is arciferal, the precoracoid and coracoid being widely 

 separated medianly, and connected by a large arched epicoracoid, over- 

 lapping its fellow. 



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 is shaped like a V, or like a pair of 

 tongs. The ends 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. Ilium, ischium, and pubis unite 

 in bounding the deep socket or acetabulum with which the 

 femur articulates. 



The skeleton of the hind-limb consists of a thigh bone or 

 femur, a lower leg formed from the united tibia and fibula, 

 an ankle region or tarsus including two long proximal 

 elements — the astragalus or tibiale and the calcaneum or 



