THE ELASMOBRANCH FISHES 



153 



IMi®. 



ib.m.j. 



e.b.= 





eb. 



.a.b 



_w-.efc. 



::;^.._b.r. 



The finer structure of the gill of Torpedo shows that the relation of the blood 

 system to the gill is much like that of Mustelus and Heptanchus. Passing 

 through the base of the septum, and anterior to the cartilaginous branchial 

 ray (b.r.), is an afferent ])ranchial artery ((//.)• From this an arteriole (a.h}) 

 passes to the anterior filament and another (a.h.-) to the posterior filament. 

 These arterioles give off smaller l)ranches which break u)) into a net of capil- 

 laries which, in turn, form a complex web over 

 the larger ])art of the surface of the filament. 

 The capillaries are continued to efferent bran- 

 ehials {e.h.^ and e.h.^) as efferent arterioles 

 which carry the oxygenated blood down the 

 filament into the efferent-collectors (efc), an 

 anterior and a posterior of which are present 

 at the base. 



In the spiracular pocket as in branchial 

 pockets the anterior wall is usually also pro- 

 vided with filaments. These are numerous in the 

 rays but few in number in the sharks, as in Het- 

 erodontus. In a type like Carcharias, in which 

 the spiracle is minute or wanting, they are en- 

 tirely absent. 



From the anteromedial wall of the spiracular 

 pocket and dorsally located there is an evagina- 

 tion which may reach the auditory capsule and 

 be attached to it above the postorbital groove 

 (dc, SciiUiuni, fig. 146, Mustelus, Gaelus, 

 Squatina, Rhinobatis, Zygaena). At its begin- 

 ning the diverticulum may be practically closed 

 (Oaleus), but as it approaches the auditory 

 capsule it becomes enlarged. In Squalus acan- 

 thias, Norris and Hughes (1920) have recently 

 shown that this evagination may be divided 

 into two or three diverticula each of which is 

 supplied with a branch of the ramus oticus 

 VII nerve. The organ is considered to be a 

 modified ampulla of Lorenzini. A second diver- 

 ticulum on the anteromedial wall of the spiracular pocket is located ventrally 

 near the union of the pocket with the pharynx. This in ScylUum is shallow, 

 but in some of the other Selachians it is connected to the spiracular pocket by 

 a neck. In the spiracle of rays there is a well developed valve on the anterior 

 side of the cleft. It is composed of a stiff crescentic fold of connective tissue 

 which is constantly opened and closed in respiration. Serving as a support for 

 the fold is the strong crescentic spiracular cartilage which at each end is fixed 

 by ligament. The closure of the spiracle is due to the contraction of the first 



-ad. 



C 



Fig. 14.5. Section of branchial 

 filaments, parallel to branchial 

 ray. Torpedo. (From Droscher.) 

 a.b.^~-, afferent branchial ar- 

 terioles from afferent artery; 

 ad., adductor muscle; af., affer- 

 ent artery; h.r., branchial ray; 

 e.b.^~-, efferent branchial arte- 

 rioles to efferent-collectors ; efc, 

 efferent-collector; ih.m., inter - 

 branchial muscle. 



