The elasmobranch fishes (1934) The elasmobranch fishes elasmobranchfish03dani Year: 1934 THE ELASMOBRAN(!II FISHES 37 A transverse section tliroiig'h the sting of Vrolophus (p. 29, fig. 32) sliows tliat it is convex dorsally. The ventral side consists of right and left plane surfaces separated by a median ventral ridge. Both the plane surface and the convex dorsal sides are covered with a thin layer of enamel (e.) under which is the thick dentine {d.). But the dentine here is arranged differ- A ently from that of the placoid scale. I I Figure 43 is drawn from the dorsal side of a sting and re
The elasmobranch fishes (1934) The elasmobranch fishes elasmobranchfish03dani Year: 1934 THE ELASMOBRAN(!II FISHES 37 A transverse section tliroiig'h the sting of Vrolophus (p. 29, fig. 32) sliows tliat it is convex dorsally. The ventral side consists of right and left plane surfaces separated by a median ventral ridge. Both the plane surface and the convex dorsal sides are covered with a thin layer of enamel (e.) under which is the thick dentine {d.). But the dentine here is arranged differ- A ently from that of the placoid scale. I I Figure 43 is drawn from the dorsal side of a sting and represents it as a transparent object. In it may be observed numerous longi- tudinal and anastomosing canals (r.) surrounded by heavy dentine (f/.). This arrangement of canals is much like that which we have observed in the saw tooth of Prist is. The sting is clearly a protective structure. In those rays in which it is attached nearer the body, as in Myliobatis, it is more effective than in types like Dasyafis, in which it is located farther out on the tail. In either type, the sting is brought into action by thrusting the tail upward and forward over the back. In the thrust the weapon is driven forward with precision and force, and is removed with great difficulty from the wound, the recurved hooks (sp.) forming a most painful tearing surface unless the sting can be pushed en- tirely through. Gill Rakers lii Fig. 42. Sting of sting rav. In some forms, structures internal branchial arches rakers, such, for ex- ample, as are seen in Squalus sucklii (p. 154, fig. 147, gr.). These gill rakers evidently serve as .strainers to prevent food from passing out with the respiratory current. Structures somewhat like these in function but very unlike them in form have become remark- ably specialized in Cf^or/rnnrs »(fl,r('- nius ( ) and in Rhinodon typi- cus, in which they form a highly complex straining apparatus. Each raker in Ceiovliinus arises from a semilunar base and extends as
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