378 



THE DOGFISH 



is largely replaced. Much of it, however, remains as the 

 gelatinous intervertebral substance. The notochord is one 

 of the most characteristic organs of the Vertebrata. 



The skeleton of the median fins consists of a series of 

 parallel cartilaginous rods, the fin-rays or pterygiophores 



art/ 



Fig. 102. — Ventral view of pectoral arch of Scyllium with right 



pectoral fin. 

 The pectoral arch is divisible into dorsal (pet. g) and ventral (pet. ^) 

 portions separated by the articular facets (art. f) for the fin. 



The pectoral fin is formed of three basal cartilages (hs. 1-3) and 

 numerous radials (rod) ; its free edge is supported by dermal rays (d.f. r). 

 (Modified from Marshall and Hurst.) 



(Fig. 99, Ptgph), the proximal ends of which are more or 

 less fused together to form basal cartilages or basalia. The 

 free edges of the fins are supported by a double series of 

 delicate horn-like fibres, the dermal fifi-r ays {Derm. F. R). 

 The shoulder-girdle (Fig. 1*02) is a strong, inverted arch of 



