THE ELASMOBRANCH FISHES 205 



elongated and tapers gradually towards the tail, the last five 

 inches of which are bent upwards at an angle. The body is 

 furnished with certain flattened expansions of the skin, sup- 

 ported by horny and cartilaginous rays. These fins are very 

 important structures, and will be described in detail in connec- 

 tion with the skeleton. For the present it is sufficient to note 

 that there are four unpaired or median fins and two pairs of 

 lateral fins, the latter representing the limbs of the higher 

 vertebrates. The anterior dorsal fin is placed rather far 

 back in the mid-dorsal line of the body; in a specimen 

 22 inches in length the front edge of the anterior fin was 

 ii inches, and the posterior dorsal fin 15 inches from the 

 snout. The caudal fin forms a vertical expansion round the 

 posterior five inches of the tail. It starts on the dorsal side 

 as a low ridge, gradually increasing in size to the tip of the 

 tail, round which it is continued into the ventral lobes. The 

 ventral part of the caudal fin is deeper than the dorsal part, 

 and is partially subdivided into two lobes, of which the 

 anterior is considerably the larger. The ventral median fin is 

 situated in the mid-ventral line, some three inches behind the 

 cloacal aperture and opposite to the interspace between the 

 two dorsal fins. On removing the skin from one of the 

 median fins it will be noticed that the greater part of its extent 

 is simply a fold of the integument supported by a large number 

 of very fine horny fin-rays, but its base is thickened and 

 muscular, and supported by a smaller number of cartilaginous 

 fin-rays. 



The anterior pair of lateral fins are known as the pectorals. 

 They are large triangular expansions attached by their apices 

 to the ventro-lateral margins of the body not far behind the 

 head. In a specimen 22 inches long the anterior edge of the 

 pectoral fin was 3^ inches from the tip of the snout. The 

 posterior or pelvic pair of lateral fins are smaller than the 

 pectorals, and rise from near the middle line of the body just 

 in front of the cloacal aperture. In the female the pelvic 

 fins are sub-triangular in shape and their inner margins are 

 free ; but in the male the inner margins are fused together, 

 and below the sort of hood thus formed there project a pair 

 of stout styliform processes, deeply grooved along their inner 

 edges, and furnished with a terminal tuft of papillae. These 

 are the accessory male organs or claspers, used in copulation. 



