119 



generally agree with those of Laemargus , one of them, — the hyo- 

 mandibular — presents in Raia a remarkable extension over both 

 aspects of the greatly expanded pectoral fin. By this extension of the 

 hyo-mandibular (which is found in the shark-like rays as well as in 

 the greatly specialized Torpedoes) , the skates and rays can be readily 

 distinguished from the sharks. 



The supra-orbital canal, beginning in connection with the infra- 

 orbital and lateral canals, proceeds forwards to the tip of the snout 

 which it pierces, and then runs backwards and outwards, to terminate 

 by opening into the infra-orbital canal , after forming a long prenasal 

 loop. The dorsal part of the canal gives off twenty-three tubules 

 — arranged in three separate groups — and receives thirty-six nerves, 

 twenty of which reach the rostral part of the canal , which has no 

 direct communication with the surface. The ventral part opens to the 

 surface by twenty-two very short tubules , and receives thirty-six ner- 

 ves , which , like those for the dorsal part , come from the superficial 

 ophthalmic division of the facial. 



The infra-orbital canal, beginning like the supra-orbital at the 

 anterior end of the lateral canal, runs outwards and forwards external to 

 the eye, pierces the snout and then runs backwards; and, after com- 

 municating with the supra-orbital and hyomandibular, runs outwards 

 behind the nasal capsule to meet its fellow of the opposite side in front 

 of the mouth. Leaving its fellow, it runs forwards to again unite with 

 it at the tip of the snout. The dorsal part gives off a large tubule as it 

 bends forwards under the eye, and twelve tubules, four of which open 

 into a dorsal extension of the hyomandibular canal. The ventral part 

 opens to the surface by thirty-seven tubules, the majority of which 

 are extremely short, owing to the canal being partly embedded in 

 the skin. 



The dorsal part of the canal receives in all twenty-five branches ; 

 while the ventral part receives sixty-six branches from the buccal 

 nerve, some of the branches springing from the main trunk, some from 

 the inner and some from the outer divisions of the buccal division of 

 the facial. 



The hyomandibular canals bear in their extent a relation to the 

 greatly expanded pectoral fins. Beginning in front connection with 

 the infra-orbital , each canal runs backwards , beyond and external to 

 the branchial clefts, to form a well-marked ventral loop, the outer limb 

 of which passes to the dorsal surface ; and after expanding, runs back- 

 wards to open into the long scapular offshoot from the lateral canal. 

 From the ventral portion of the hyomandibular canal only fourteen 

 tubules spring , the dorsal part has four of the infra-orbital tubules 



