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canals. We hence adopt the term of sensory canals 
originally proposed by Ewart. 
Now the sensory canals are not 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 R. 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 superficialis vii.; the 
infraorbital canal under the eye, defined by the R. 
bucealis 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 
