THE DOGFISH 



34 1 



General 

 Internal 

 Features 



downwards. The vent or opening of the cloaca 

 deep longitudinal groove of the belly, 

 just before the middle of the body. 

 Into the same groove there opens at 

 each side one of the abdominal pores, 

 which lead from the body cavity. There 

 are two pairs of fins and four unpaired 

 fins. The fore or pectoral fins, corre- 

 sponding to the arms of the frog, are a 

 pair of flat, triangular organs attached 

 by one angle to the sides of the ventral 

 surface not far behind the head. The 

 hinder or pelvic fins are smaller and 

 narrower structures of somewhat the 

 same shape, attached one on each side 

 of the middle line of the belly in front 

 of the vent. In the male, their inner 

 edges are fused and there projects back- 

 wards from the under surface of each a 

 rod, grooved along its inner side, known 

 as a c/asper. The unpaired fins are 

 median structures in the tail. Two, 

 known as the anterior and posterior 

 dorsal fins, are on the back, one, the 

 ventral fin, is on the under side, and 

 another, the caudal fin, surrounds the 

 end of the tail. This fin has two lobes, 

 and the axis of the tail is turned upwards 

 and passes into the upper lobe. 



Certain generalisations which we have 

 made in the course of the 

 previous chapters enable us 

 to state in a few words a 

 good deal of information 

 about the anatomy of the dogfish. A 



lies 



FlG. 245. — The Rough Hound. 



Note mouth, eye, spiracle, lateral line, gill clefts, 

 pectoral and pelvic fins, dorsal fins, caudal fin, 

 ventral tin between caudal and pelvic fins. 



c.f., Upper lobe of caudal fin; c.f ., lower lobe of the 

 same ; pt'f-, right pelvic fin. 



