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Show 282 MB. W. E. COLLINGE ON THE [Apr. 2, mandibular branch of the main sensory canal, it also communicates with the facial. The ramus internus passes on the inner side of the jaw to the mandibular barblets, &c. I failed to trace any branches of the ramus mandibularis passing to the maxillary barblet (cf. Ramsay Wright, 13. p. 368). 6. The ramus oticus is larger in Amiurus catus than in any of the types previously mentioned. It arises in close conjunction with the ramus ophthalmicus superficialis, passing from the brain through a foramen in the sphenotic. The most dorsal branch innervates the main canal; below this two other branches pass off, while the fourth or main branch passes to the upper portion of the sensory canal in the hyomandibular (Ramsay Wright says preoperculum). The innervation of this branch of the main canal by the ramus oticus is of special interest, as in most other fishes it is innervated by a branch of the facial nerve. Professor Ramsay Wright (13. p. 366) was the first to describe the distribution of this nerve in Amiurus. The Facial Group.-~No portion of the facial nerve, so far as I have been able to trace, innervates any portion of the sensory canal system. As previously pointed out, the descending branch of the ramus oticus replaces the hyomandibular branch of the facial in the upper portion of the operculo-mandibular canal, while the lower portion is innervated by the ramus mandibularis of the trigeminal, the mandibularis of the facial lying below it. The Glossopharyngeal.-I have not been able to trace any connection between this nerve and the sensory canal system, although it seems very probable that the most posterior portion of the main canal of the head is innervated by it. The Vagus.-The ramus lateralis vagi leaves the main branch just below the ganglion and passes posteriorly over the supra-clavicle (McMurrich); just behind the ascending process of the supra-clavicle it gives off two branches, one passing above to the occipital commissure and the other laterally to the branch x (PI. XVIII. fig. 2, I & T). 3. PIMELODUS MACULATUS. General Description. The sensory canal system of Pimelodus has not hitherto been investigated. Pollard (11) has described and figured that in Auchenoglanis biscutatus, a species of an allied genus. In Pimelodus the lateral canal commences at the base of the caudal fin, and passes forwards as a direct line to the region of the head. From its commencement to where the canal passes over the transverse processes of the fourth and fifth vertebrae, which are here developed to an unusual extent (cf. Bridge and Haddon, 2. pp. 119-25), there are from 85 to 95 pores, varying in number according to the age of the fish. In the region of the fourth and fifth vertebrae, the canal gives off two branches, one on either side of the canal, and from these a series of smaller branches and |