OCR Text |
Show 1895.] SENSOEY CANAL SYSTEM OF FISHES. 295 1. The ramus ophtlialmicus superficialis is the first branch passing from the Gasserian ganglion. It is covered for a part of its course by the branches of the olfactory nerve. It arises from the ventral side of the G-asserian ganglion and gives off a series of fine branches, which innervate the supra-orbital branch of the main sensory canal (PI. X X I . figs. 16, 17). 2. The ramus buccalis innervates the anterior portion of the sub-orbital branch of the main sensory canal. Its distribution is somewhat different from that figured and described in Esox. It divides posterior to the orbit into two branches, both of which pass forwards to the region of the snout. In Esox this division takes place anterior to the orbit. 3. The ramus maxillaris together with the ramus mandibularis forms the main branch of the trigeminal nerve. It passes forwards and downward towards the orbit, on the border of which it divides, sending a branch (PI. X X I . figs. 16,17 r.mxf) to the posterior and inferior portions of the sub-orbital branch of the main sensory canal; this again divides, forming the branch r.mx.2 (fig. 17) which innervates the saccular dilatation number 4. The ramus mandibularis does not innervate any portion of the canal system. 4. The ramus oticus innervates the whole of the main canal of the head. It consists of two main divisions, which further divide into numerous fine twigs. The Faded nerve innervates the terminal portion of the lateral canal and the operculo-mandibular branch of the main canal. The chief division, represented in Esox by the ramus hyomandibularis (PI. X X . figs. 10, 11, r.hy.), is somewhat different in Conger (PI. X X I . figs. 16, 17, r.hy.). Below the lateral border of the frontal bone, and upon the upper portion of the hyomandibular bone, it divides into two main branches; the smaller (fig. 17, r.op.) passes posteriorly beneath the opercular portion of the sensory canal. Its main branch is continued backwards for some little distance and innervates a large sensory organ in the saccular dilatation number 1, and the last sensory organ in the lateral canal. The two smaller divisions do not innervate any portion of the canal system. The larger branch, the ramus hyomandibularis (fig. 20, r.hy.rm.), passes along the side of the operculo-mandibular branch of the main sensory canal and divides into a mandibular and hyoidean branch. Branches from the former pass to the lower part of the opercular portion of the operculo-mandibular branch, to the saccular dilatations numbered 2 and 3, and also to the mandibular portion of the canal. The Glossopharyngeal Nerve.-I have been unable to trace any portion of this nerve to the main canal. It seems, however, to replace the anterior and dorsal branches of the vagi lateralis and innervates the two sensory organs in the occipital commissure. The Vagus is very similar to that described in Esox, excepting that there are no anterior branches given off from the vagi lateralis. |