THE ELASMOBRANCH FISHES 



95 



from tlie basal and radial cartilages, and extend outward to be attached to the 

 connective sbeath of the ventral side of the fin. 



The muscles governing the clas])ers of the fins in the male are in bundles 

 specialized from dorsal and ventral radial mus- 

 cles. We may first examine them on the dorsal side 

 of the pelvic of the male (fig. 96). Here they are 

 continued from the myomeres to the fin, parallel 

 with the radials, and are firmly attached to the pe- 

 ripheral part of the fin skeleton. The first of these 

 muscles is the adductor (ad.), which arises from 

 the posterior border of the pelvic girdle and is 

 inserted on the distal end of the basipterygium 

 (see p. 50, fig. 55b, ha.p.). The external flexor 

 muscle if.e., fig. 96), which has its origin along 

 the inner margin of the basipterygium {ha.p.), is 

 inserted on the "beta" cartilage (B, fig. 55b). In 

 Heptanchus the internal flexor (f.i.) arises in 

 common with, but deeper than the external flexor 

 on the basipteryginm and on the "beta" cartilage 

 and is inserted on the segment 6- (fig. 55) and on 

 the proximal part of the basal cartilage (ba.) . On 

 the dorsal side are also to be seen the dilator (dl.) 

 and the compressor (cp.) muscles. The dilator 

 arises on the proximal end of the basal cartilage 

 (ha.) and is inserted distally with the connective 

 tissue covering the tip of the basal cartilage. The 

 compressor muscle (cp.) has its origin from the 

 "beta" cartilage (/8, fig. 55b) , and passes backward 

 and outward to be inserted on the last radial car- 

 tilage. One of the muscles associated with the 

 clasper, which is not seen in dorsal view, is the 

 constrictor of the sac. Its fibers arise from the seg- 

 ments &.^"-, and from the proximal end of the basal 

 cartilage. Its dorsal fibers are inserted on the curved radial and its ventral 

 fibers form the wall of the pterygopodial sac. 



Fig. 96. Muscles of the pelvic 

 fin of male, Heptanchus mac- 

 ulatiLS, dorsal view. (From 

 Davidson.) 



ad., adductor muscle of 

 clasper; cp., compressor of 

 the sac ; dl., dilator muscle ; 

 f.e., external flexor muscle; 

 f.i., internal flexor; p?., pelvic 

 girdle; ra., radial muscles; 

 s.m., muscle of sac. 



