156 ME. F. J. COLE ON THE STRUCTURE AND MORl'HOLOaY OF 



M. Innervation of the Sensory Canals in Gadus. (Plate 22.) 



(1) Supni-orhital Canal. 



Superficial Ophthalmic Trunk. — This consists of two portions, which are {a) the 

 supei-ticial ophthalmic of the trigeminus, and {b) the superficial ophthalmic lateral line 

 nerve. The latter arises from the posterior dorsal edge of the proximal portion of the 

 lateral line ganglion, and at its origin lies between the ventral edge of the cerebellum and 

 the anterior extremity of the auditory capsule. Owing to a certain amount of over- 

 lapping on the part of the facial and auditory nerves, the origin of the lateral oplithalraic 

 nerve is somewhat difficult to determine, owing to the close apposition of its root to the 

 anterior edge of the auditory ganglion. It would in fact be difficult to say whether some 

 auditoi'y fibres did not mingle with the lateral ophthalmic. There are a few ganglion 

 cells at its base, but otherwise no cells whatever in the course of the nerve, and the few 

 above belong, strictly speaking, to the lateral ganglion. 



The lateral ophthalmic now passes horizontally forwards over the trigemino-facial 

 ganglion and soon commences to pass upwards. As, however, it leaves the ganglion, it 

 receives a conspicuous root containing a few ganglion cells from the anterior dorsal edge 

 of the ganglion, and this is the root of the trigeminal ophthalmic, since it is from the 

 direct continuation of this portion of the trunk that the general sensory fibres arise. The 

 root of the trigeminal ophthalmic is at first very flat, and closely opposed to the ventral 

 surface of the lateral ophthalmic root, but no mingling of the fibres coidd be detected 

 either at this region or any other. 



As the trunk passes gradually upwards towards the posterior poi'tion of the infra- 

 orbital canal, the trigeminal portion becomes narrower and is almost completely separated 

 from the lateral portion by a small blood sinus or vessel. Fui'ther forwards, however, 

 the two nerves become approximated by passing under this vessel. By this time the 

 nerve has entered what appears to be a rudimentary eye muscle canal, and lies opposite 

 the ventral edge of the alisphenoid over the posterior portion of the eye, and (iu the 

 young forms but not in the adult *) somewhat close to the brain opposite the dorsal 

 border of the optic thalami and the origin of the optic nerves. The twig to the fifth 

 sense organ of the supra-orbital line is given off from the dorsal or lateral portion of the 

 trunk at this region. It perforates the wall of the eye muscle canal, passes upwards and 

 forwards to the outside of the alisphenoid, finally piercing the frontal to reach its 

 distribution. 



Continuing its course, the ophthalmic trunk passes obUquely upwards and assumes a 

 position between the dorsal border of the eye and the supra-orbital canal. Soon after 

 supplying the twig to sense organ 5, the lateral ophthalmic gives off a somewhat large 

 branch [S.O.^) which, after coursing parallel with the main trunk for a short distance, 



* The rc4atioiis are by uo meaus the same. Fur example, a trausverse section may pass through both the optic 

 lobes and a portion of the eye iu the young forms, whereas in the adult no such section could pass through a»y part 

 of the lirain and eye at the same time. 



