The elasmobranch fishes (1934) The elasmobranch fishes elasmobranchfish03dani Year: 1934 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 elasmobranch fishes (1934) The elasmobranch fishes elasmobranchfish03dani Year: 1934 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 can
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