J520 



THE DOGFISH. PHYLUM CHORDATA 



FINS 



The median tins are supported by a skeleton consisting of 

 several series of rays. The series nearest the body are cartilaginous 

 rods known as basalia and are attached to the neural and haemal 

 spines. They are succeeded by a similar series known as radialia, 

 and those by two rows of small, polygonal plates of cartilage 

 which are overlapped at the sides by a double series of horny 



cor 



, . ventra-l su.ria.ce 



Fig. 241. — A ventral view of the skeleton of th^ pectoral girdle and pectoial 



fin of a dogfish. 



cor ., Coracoid region ; dors., dorsal end of scapula ; gl., glenoid facet ; h.r., horny rays (dermotrichia) ; 

 except on the outer border of the fin shown these have been cut away where they covered the cartila- 

 ginous rays ; mpt., metapterygium ; mspt., mesopterygium ; ppt., propterygium ; rad., cartilaginous 

 rays ; sc, scapula. 



rays or dermotrichia that project beyond them. The dermotrichia, 

 which belong to the dermis, are fine fibres composed of the same 

 substance (elastin) as the elastic fibres of connective tissue 

 (p. 514). In the caudal fin the cartilaginous rays are not distinct 

 from the supradorsals and haemal spines. 



The limbs are anchored into the body by girdles which corre- 

 spond to those of man, though neither is attached to the backbone. 

 The pectoral or shoulder girdle (Fig. 241) consists of a single 

 nearly complete hoop of cartilage open on the dorsal aspect ; 

 it is formed in development from two cartilages, the scapulocora- 

 "'•Hs, the ventral coracoid portions of which meet and fuse in the 



