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canals. We hence adopt the term of sensory canals 

 originally proposed by Ewart. 



Now the sensory canals are nol confined to the body 

 of the fish, but always extend on to the head, where, as a 

 very general rule, they form a much more complex and 

 important system of sensory canals, which, on account of 

 their deeper situation and therefore less obvious character, 

 are too often disregarded. In the Teleostean Fishes the 

 innervation of this system is so remarkably constant in 

 those forms in which it has been properly investigated as 

 to justify its division on each side of the body into the 

 following four canals, the extent of any one of these being 

 determined by its innervation. That is to say, that part 

 of the cephalic system of sensory canals called the infra- 

 orbital canal is precisely that part of the system innervated 

 by a single perfectly definite nerve — the H. buccalis 

 facialis. One extremity of this canal is a natural blind 

 extremity, the other is the artificial boundary beyond 

 which its nerve does not extend. The four canals are : — 

 (1) the lateral canal at the side of the body (" lateral line " 

 of systematists), defined by the branching of the R. 

 lateralis vagi ; (2) the supraorbital canal over the eye, 

 defined by the R. ophthalmicus supei*ficialis vii. ; the 

 infraorbital canal under the eye, defined by the R. 

 buccalis vii. ; and the hyomandibular canal on the oper- 

 culum and lower jaw, defined by the R. mandibularis 

 externus vii. These nerves are in this work only provi- 

 sionally associated with the vagus and facial nerves, as 

 their true morphological value cannot be discussed in a 

 general treatise of this nature. 



Although much work has been done on the use of this 

 undoubtedly sensory apparatus, its function is even yet a 

 subject for speculation. This is due to the fact that 

 owing to its very diffuse nature and the intimate relations 



