ix pfiCToRAL Fin 427 



arch. On each side of its outer surface it presents three 

 articular facets for the pectoral fin ; the presence of 

 these allows of the division of each side of the arch 

 into a narrow, pointed, dorsal portion corresponding to 

 the scapular region of the frog {pet. g), and a broader 



rtf 



Fig 106. — Ventral view of pectoral arch Ot ScyUium with right pectoral fin. 

 The pectoral arch is_ divisible into dorsal or scapular i^pct. g) and ventral or cora- 

 coid ipci.g') portions separated by the articular facets {art. f) for the fin. 

 The pectoral fin is formed of three basal cartilages (bs. i — 3) and numerous 

 radials {rod) ; its free edge is supported by dermal rays id./", r). (Modified from 

 Marshall and Hurst.) 



ventral portion, answering to the coracoid {pet g) united 

 in the middle line with its fellow of the opposite side : there 

 is no sternum. The pectoral fin is formed of ptery- 

 giophores {rad), fused proximally to form basals which are 

 three in number {bs. i.— 3), fhe third, like the main 

 basal of the pelvic fin, being the largest and supporting 

 the greater number of the cartilaginous rays, which give 

 rise distally to a series of polygonal plates. 



