THE LATERAL SENSE ORGANS OF ELASMOBRANCHS. 



477 



the larger or smaller numbers of canals generally, characteristic of species relative 

 to one another. 



(l) Superficial Ophthalmic Canals. 

 The dorsal canals of the ophthalmic ampullae are distributed in two groups : 

 (l) an anterior, and (2) a posterior group, both of which lie close to and parallel with 

 the rostrum (Plate I). The canals of the anterior group are directed forwards towards 



c.w. 



Text-fig. 4. — Mandibular capsule, R. radiata. xl4. 



A. Ampulla. C.W. Capsular wall. C. Canal. 



N. Nerve. N.S. Nerve to sensory canal. 



C.W. 



N 

 Text-fig. 5. — Abnormal mandibular capsule, R. circularis. 



A. Ampulla. C.W. Capsular wall. 



C. Canal. N. Nerve. 



xl4. 



the tip of the snout ; those of the posterior group are directed backwards to a point in 

 front of and slightly to the inner side of the anterior corner of the eye. These canals 

 were overlooked by Sappey, who described a species of " la raie " to which he gives no 

 specific name. He expressly states that canals arising from his "cephalic glands" 

 (ampullae of the cephalic region) open on the ventral surface only, and in his figure 

 of a dissection of the dorsal surface canals are represented arising from the hyoid 

 ampullae only. Similarly, G-arman, in his paper on the lateral canal system, omits 

 them from a figure of the ampullary canals of Raia Isevis which he gives for purposes 

 of comparison with the sensory canals. 



