Proceedings of the general meetings for scientific business of the Zoological Society of London, 1895

Page 996

882 MR. WALTER E. COLLINGE ON THE SENSORY [Dec. 17, 4. Innervation. In view of recent researches upon the innervation of the sensory canal-system in fishes, the results obtained in Chimcera are ex­ceedingly interesting and quite unlike what I expected. Until quite recently it was generally assumed that the inner­vation of the sensory canal-system in fishes proceeded from the trigeminal group of nerves. Ewart (6 & 7), w h o was the first to carefully investigate this matter in the Elasmobranchii, has shown that the whole system is innervated by the facial complex, ramus oticus and vagus, " the fifth taking no part in innervating the canals." In the Ganoidei, Allis (1) and others have shown that this innervation still obtains, supplemented in Polyodon (3) by the trigeminal. In the Teleostei (5) the facial is almost entirely replaced by the trigeminal group ; and, judging from comparative smallness of the branches of the facial in Protopterus (13) and Lepidosiren, we may safely assume that the fifth also innervates the canals in the Dipnoi. Erom the nature of the skeleton, the fact that the sensory canals persisted as open grooves, and the presence of ampullary canals, in all three features showing a close affinity with the Elasmobranchs, I expected to find an innervation solely from the facial; but the condition which actually exists is just the reverse, for w e find an enormous development of the branches of the trigeminal nerve, particularly of the ramus ophthalmicus superficialis and profundus and ramus buccalis. Before describing tbe distribution of the nerves I would point out that Stannius (17), as early as 1849, stated that in Callorhyn­chus certain parts of the canals were innervated by the ramus buccalis and ramus maxillaris superior of the fifth nerve. The Trigeminal Group consists of the following main branches :- 1. The ramus ophthalmicus superficialis. 2. The ramus ophthalmicus profundus. 3. The ramus buccalis. 4. The ramus maxillaris. 5. The ramus mandibularis. 1. The ramus ophthalmicus superficialis is the most dorsal and anterior branch. Previous to entering the orbit it joins with tbe facial by a commissure (PI. LII. fig. 7, V. com.), and some little distance in front of this joins with the branch which on entering the orbit divides into the ramus buccalis and ramus maxillaris. The superficialis passes across the orbit and through a foramen at the opposite side. In its course across the orbit it gives off six dorsal branches. 2. The ramus ophthalmicus profundus passes beneath the two commissures referred to above and below the superficialis. Ante­rior to the orbit both superficialis and profundus anastomose and then break up into a multitude of fine branches, which innervate the supra-orbital branch of the main sensory canal of the head. (PL LII. fig. 7.)