THE ELASMOBRANCII FISHES 51 



The pelvic girdle (pi., fig. 55) is a flattened band of cartilage, slightly con- 

 cave dorsally and enlarged at the ends. Perforating the terminal parts of the 

 girdle are from one to three foramina (see p. 95, fig. 96) through which nerves 

 pass to the pelvic fin. At the termini of the girdle are the articular processes, 

 each consisting of two protuberances which fit into depressions (fossae) of the 

 pelvic fin skeleton. These are not well shown in figure 55. 



Fig. 56 Fig. 57 



Fig. 56. Dorsal fin, Heptanchus cinereus. (From Mivart.) 

 Fig. 57. Anal fin, Heptanchus cinereus. (From Mivart.) 

 Z)c., basal cartilage ; ra., radial. 



The framework of the pelvic fin proper consists of a long posteriorly pro- 

 jecting basal cartilage, the basipterygium {ha. p.) which bears one or two 

 small terminal segments. From this cartilage in the female proceed 21 or 22 

 radials {ra., fig. 55a), all of which, except the last five, are segmented. Ante- 

 riorly, a much enlarged plate meets the basal piece, forming an obtuse angle. 

 From this run three rows of radials. At the proximal ends of this enlarged 

 plate and the basal piece, are the two fossae with which the protuberances on 

 the pelvic girdle above described articulate. 



In the male the long basipterygium {ha.p.) is continued bj^ the basal or axial 

 cartilage of the claspers {ba.). Where the two join there are two segments 

 (&.^"-), and dorsal to them is the so-called beta cartilage (^) . 



Skeleton of Unpaired Fins 

 DOESAL FIN 



Extending over the forty-ninth to the fifty-fifth segment of the vertebral col- 

 umn is the thin basal cartilage of the dorsal fin (see Heptanchus cinereus, 

 fig. 56, be). From this plate in Heptanchus maculatus arise seventeen or 

 eighteen radial cartilages {ra. ) , one of which, the anterior, is unsegmented and 

 a few of the posterior radials may or may not be fused into a single piece. 



CAUDAL FIN 



The segments of the tail show a characteristic diplospondyly in the arches 

 both above and below the central column, although the pseudosegments of the 

 central column itself are not doubly constricted. The ventral rays of the caudal 



