XII 



PHYLUM CHORDATA 



415 



Passing forwards from the anterior ends of the united 

 epicoracoids is a rod of bone, the episternum {Ep), tipped 

 by a rounded plate of cartilage, the omosternum ; and passing 

 backwards from their posterior ends is a similar but larger 

 bony rod, the sternum {St), also tipped by a cartilaginous 

 plate, to which the name xiphisternum (K?i) is applied. 



Fig. 249. — Rana esculenta. The shoulder girdle from the ventral aspect. Co, 

 coracoid: Co', epicoraeoid; CI, clavicle; G, glenoid cavity; £/>, episternum; 

 Fe, fenestra between procoracoid and coracoid; KC, cartdage separating scapula 

 and clavicle; A'ti, xiphisternum; m, junction of epicoracoids; S, scapula; 

 St, sternum. (From Wiedersheim's Comparative Anatomy.} 



The four limbs deviate from the typical structure (p. 341) 

 chiefly in the fusion of the radius and ulna into a single 

 radio-ulna (Fig. 247, RA. UL) and in the presence of only 

 four complete digits with a vestigial one on the radial side. 

 In all probability the latter represents the pollex, and the 



