SENSORY CANALS OF L^MARGUS. 



67 



division of the facial, represents the cranial (cr.), rostral (r.), and subrostral (sr.) canals 

 of Garman (tigs. A and B). Garman figures and describes the cranial (first portion of 

 the supra-orbital) as beginning in front of, and distinct from, the orbital (orb., fig. A), i.e., 

 the first portion of infra-orbital. This view I was at first prepared to accept ; but on 

 cutting into the canals, I found that they not only communicate with each other, but 

 open to the exterior by a common pore. 



The course of the supra-orbital canal will be best understood by a reference to 

 figure 1 (PL I.). Beginning 3*25 cm.* in front of the auditory pore, and 1 cm. from the 

 middle line, it first bends outwards and forwards, and then forms a wide open curve 

 (S.O. 1 ), within which lie the openings of numerous ampullary canals. 



On approaching the region of the nasal capsule, the canal runs inwards and then 

 forwards to perforate the snout, about 2^ cm. from the middle line, and 1 cm. behind its 

 anterior margin. Turning sharply backwards, it runs outwards, and then returns to the 

 dorsal aspect (S.O. 3 ), arching over the nasal capsule to again reach the ventral surface ; 

 where, after curving first inwards and then outwards, it terminates (S.O. 4 ) by communi- 

 cating with the infra-orbital canal (I.O. 2 ). 



The supra-orbital canal has, throughout the greater part of its length, a diameter of 

 from 3 to 4 mm. ; but the first 3 or 4 cm., and the portion which curves over the 

 nasal capsule, are only from 2^ to 3 mm. in diameter. The walls of the canal are from 1 

 to 1| mm. in thickness. The canal not only varies in diameter, but also in its relation 

 to the skin. Some parts lie in contact with the skin ; while others lie embedded, some 

 distance from the surface, in the subcutaneous tissue. Usually, the portions in contact 

 with the skin have a smaller calibre than the portions lying deeper. Beginning in 

 contact with the skin, the canal, when about 3 cm. from its origin, sinks to a distance of 

 4 mm. When on a level with the nasal capsule, it lies 6 mm. from the surface ; and the 



* The measurements refer throughout the paper to a fish that had a total length of 11 feet. 

 VOL. XXXVII. PART I. (NO. 5). M 



