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Show 294 . ME. W. E. COLLINGE ON THE [Apr. 2, 3. The OCCIPITAL COMMISSUBE passes off as an inward branch immediately in front of the lateral canal, and almost opposite to the operculo-mandibular branch (PI. X X I . figs. 16, 17). Like all the other branches, it is enclosed in a series of more or less isolated cartilages. It traverses the occipital region of the head and forms a connection between the main canals of either side of the head. The distribution and branching of the sensory canal system in Conger conger resembles in a many ways that figured in Clarias. The large saccular dilatations are perhaps the most peculiar feature in connection with the form of the canal, etc., but branches occur in Clarias in these several positions. This form of canal has not previously been described in the Physostomi, I believe, and it cannot be regarded as at all typical of this suborder. Leydig (6) was the first to draw attention to these peculiar cartilages enclosing the canals of this form, and in 1850 he figured and described them in Lota vulgaris. I shall have to refer to this account later when treating of the suborder Anacanthini and to compare it with Hyrtl's account and some investigations of m y own. O n PI. X X I . figs. 18, 19, I have figured the cartilage which connects the occipital commissure with the large saccular dilatation, from which the main canal of the head and the operculo-mandibular branch pass off. Each cartilage forms a drainpipe-like structure, averaging from 20 to 44 millim. in length, the walls of w7hich consist of a dense connective tissue, with numerous cartilage cells scattered throughout. Towards one end and on one side of the cartilage a series of white patches are present, which remind one of the terminal cartilages on the bronchial tube of many vertebrates; these are denser patches of cartilage. On the dorsal surface and towards the end not possessing these cartilaginous patches is a small ossification. This was not found to be present on all the cartilages. Each cartilage is connected with its fellow by a prolongation of the connective tissue, as shown in figure 18, these overlapping the sides of the cartilage at the end, a, fig. 19. The presence here of a dense connective tissue, isolated chon-drifications, and an ossification afford an interesting example of the manner in which canal-bones m a y have originated. Innervation. The specialization in the form of the sensory canals, as has been described in Conger, is accompanied by a greater development of the cranial nerves and an increase in the branching. The nerves of the trigeminal group are all large branches, and, excepting the ramus oticus, pass forwards. The branches which innervate the canal system are :- 1. The ramus ophthalmicus superficialis. 2. The ramus buccalis. 3. The ramus maxillaris. 4. The ramus oticus. |