282 MR. W. E, COIiLINGB ON THE [A.pr. 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. Eamsay 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 pre- 

 operculum). 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 bi-auch 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. 



TJie 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. PiMELODirS MACULATTTS. 



General Description. 



The sensory canal system of Pimeloclus 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 (r/. 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 vertebrifi, the canal gives off two branches, one on either side 

 of the canal, and from these a series of smaller branches and 



