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Show 1895.] SENSOEY CANAL SYSTEM OF FISHES. 289 side of the head. A similar series of grooves are present in the nasal region, these entering into connection with the terminal pore of the supra-orbital branch of the main canal. There is no anastomosis of the grooves of one side with the other. Innervation. In describing the cranial nerves of the Selachoid Ganoids (3) attention was drawn to the great development of the facial nerve. So far iu the Physostomous Teleosts the trigeminal has been the larger, and this is perhaps more evident in Esox lucius than in any type previously described. The sensory canal system is innervated by the same four groups, viz. the trigeminal, facial, glossopharangeal, and vagus. TJie Trigeminal Group,-The branches supplying the sensory canal system are:- 1. The ramus ophthalmicus superficialis. 2. The ramus buccalis. 3. The ramus oticus. 4. The ramus mandibularis. 1. The ramus ophthalmicus superficialis is the most dorsal branch of the trigeminal group (PI. X X . fig. 11). It passes forwards some distance above the orbit and divides into two smaller branches, which each terminate in a number of fine divisions some little distance from the snout. The nerve lies beneath the supraorbital branch of the sensory canal, to which it gives off a series of fine twigs. 2. The ramus buccalis.-The main divisions of the trigeminal are the ramus buccalis and the ramus maxillo-mandibularis; the former is the anterior and more dorsal division and passes behind and beneath the orbit, and then across the side of the face, where it divides into two, each division further dividing into a number of fine twigs which spread themselves over the terminal region of the snout. From the main branch of the buccalis a fine branch passes off to the sub-orbital branch of the main sensory canal, giving off a series of fine twigs to the sensory organs (PI. X X . figs. 10, 11). 3. The ramus oticus arises in close proximity to the ramus ophthalmicus superficialis. It passes posteriorly and divides into two, the dorsal branch innervating the main canal of the head (fig. 10, r.ot.). 4. The ramus maxillo-mandibularis is the largest division of the trigeminal group. It passes ventrally to the angle of the jaw, where it divides into internal and external mandibular branches. Some little distance above the internus the ramus maxillaris passes off (PI. X X . figs. 10, 11). The ramus mandibularis externus innervates the mandibular canal; it passes on the ventral portion of the mandible and gives off two series of fine branches, one to the canal and the other to the integument. The ramus internus divides on the inner side of the mandible into numerous smaller branches (PI. X X . fig. 12). Paoc. ZOOL. Soc-1895, No. XIX. 19 |
