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Show 1895.] SENSOEY CANAL SYSTEM OF .FISHES. 285 It crosses the ventral portion of the orbit, where a large branch passes off which is connected by a fine commissure with the ramus ophthalmicus profundus, and another with the main branch of the buccalis. The buccalis innervates all the sense-organs lying in the sub-orbital branch of the main sensory canal between the pores 18 to 24. The branches of the nerve lie dorsal to the ramus maxillo-mandibularis. 3. The ramus oticus has exactly the same course and distribution as in Clarias, innervating the anterior part of the main canal; the centre of the canal is supplied by the glossopharyngeal, and the posterior portion by branches from the lateral division of the vagus (PI. XVIII. fig. 4). The Facial, like as in Clarias, passes as a main branch through a bony canal in the hyomandibular, and after running ventrally for some short distance, divides into a ramus hyoideus and ramus mandibularis, this latter branch innervating the mandibular portion of the operculo-mandibular branch of the main sensory canal. It would appear that the mandibular rami of the fifth and seventh nerves are interchangeable as regards the innervation of the mandibular portion of the operculo-mandibular branch of the main sensory canal. Dorsal to the ramus hyomandibularis two small branches arise (PI. XVIII. fig. 4, r.d.), which do not innervate any portion of the sensory canal system and probably correspond to the branches x and y of Pollard and form the ramus dorsalis. The Vagus has a similar distribution to that in Clarias. It lies immediately behind the glossopharyngeal, but is distinctly independent of it. 4. CALLICHTHYS LITTOEALIS. General Description. The following notes have been made from an external examination of three perfect specimens and the body of a fourth. As I have not been able to inject the canals of the head or to examine the skull in detail, the specimens I examined being required for other purposes, I cannot criticise the account given by Pollard (11. p. 533). It should, however, be borne in mind, when comparing his figure (pi. 36. fig. 4) with that given on PI. X I X . (fig. 6), that the specimen he investigated was a young one only 3 cm. in length. 1. T H E L A T E E A L C A N A L commences by a pore at the base of the fin-rays of the caudal fin. It passes forwards as a dermal canal until it reaches the fifth dorsal shield from the head, which it enters and is conducted forwards through the fourth, third, and second, passing into a small canal-bone instead of the first shield. 2. T H E M A I N C A N A L may be regarded as commencing in the aforementioned canal-bone, in which it opens by two pores. Passing into the squamosal it gives off a lateral and backwardly-directed branch running from pore number 4 to 5 (PI. X I X . fig. 6). |
