172 



THE SPINY DOGFISH— THE SKATE 



the inner side of the spiracle and upper jaw, joins its fellow of the other side in 

 the middle line, then disappears in the cartilage of the skull. The second, third 

 and fourth efferent branchial vessels from the gills all converge to join the dorsal 

 aorta. Between the origin of the third and fourth pair of efferent vessels a 



Mandible 



Gills cut 

 through 



Fig. 58.— The Dogfish (AcantJiias, syn. Squalue), Efferent Branchial or Dorsal 



Arterial System. 



subclavian artery is given . off on each side, passing backwards to the 

 pectoral fin. Posterior to this the .aorta gives off the coeliac artery akeady 

 referred to. 



Make a complete drawing of the efferent branchial vessels and the dorsal 

 aorta. 



[In Scyllium the first pair of efferent vessels unite to form the aorta between the 

 first gillr clefts. At first each vessel forms a loop round the first gill-cleft. The 



