THE LIMBS AND GIRDLES. 



535 



sented. The glenoid cavity with which the humerus 

 articulates is formed as usual by the junction of scapula 

 and coracoid. 



Between the median ends of the coracoids lie two 

 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 skeleton of the fore limb consists of an upper arm 



FIG. 177. Pectoral girdle of Rana esctilenta. 

 (After ECKER. ) 



The cartilaginous parts are dotted. Ep, episternum ; om, omo- 

 sternum ; Ep.c, epicoracoids ; st, sternum ; x, xiphisternum ; c/, 

 clavicle with underlying precoracoid cartilage ; co, coracoid ; Sc, 

 scapula ' S.sc, supra-scapula ; Gl, glenoid cavity for humerus. 



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. 



