276 



THE ELASMOBRANCH FISHES 



open groove practically to the supratemporal canal, and in the notidanids it is 

 open as far forward as the anterior region of the pectoral fin. In Acanthias on 

 the contrary the canal is closed excepting in the region toward the tip of the 

 tail. In all higher Elasmobranchs it is usually closed throughout the entire 

 length. In some of these the canals run to a considerable depth, but in all such 

 they still remain in communication with the exterior by tubules. The tubules 



putting the canal in com- 

 munication with the out- 

 side may be as numerous 

 as are the branches of 

 nerves (ramuli) reach- 

 ing them (fig. 244). In 

 certain forms, however, 

 they are fewer in number. 

 In its anterior segment 

 the lateral line of each 

 side is joined to its fellow, 

 posterior to the endolym- 

 phatic ducts, by the su- 

 ]iratemporal canal (cc). 

 This canal, however, is in- 

 complete in Heptanchus. 

 Furthermore, on each 

 side it may branch so as 

 to send a part anterior to 

 the endolymphatic duets 

 in addition to the regular 

 branch posterior to the 

 ducts. In Chlamydose- 

 lachus the supratemporal 

 connection passes ante- 

 rior to the endolympha- 

 tic ducts. It seems reason- 

 able to suppose that this 

 branch is comparable to 

 the occasional anterior 

 branch of Heptanchus. 

 The lateral line canal 

 usually passes directly 

 into the cephalic canals, but in Heterodonttts francisci at its anterior end it 

 swerves sharply toward the middorsal line and joins the supratemporal canal; 

 it then joins the supraorbital canal by making a sharp bend laterally. 



The cephalic canals are usually, as we have said, a direct continuation of 

 the lateral line canal. In Laemargus (fig. 240) these canals are made up of the 

 divisions above named. The supraorbital (soc.) passes forward above the eye 



Fig. 242. The cephalic canals, Baia hatis, dorsal view. 

 (From Ewart and Mitchell, modified.) 



CO., commissural or supratemporal canal; hmc, hyoman- 

 dibular canal ; ioc, infraorbital canal ; 11., lateral line ; 

 mc, mandibular canal ; soc, supraorbital canal ; sc.'^'", first 

 and second scapular canals; sp., spiracle. 



