| OCR Text |
Show 284 ME. W. E. COLLINGE ON THE [Apr. 2, The Sub-orbital Branch is the lateral division of the main canal. It is conducted around and below the orbit by three small canal-bones. After leaving the most anterior of these the branch is continued as a dermal canal around the lateral border of the nasal capsule and terminates by bifurcating. The dendritic branching is more easily distinguishable here than on the supra-orbital branch; very "many of the branches, however, persist as grooves. The whole region of the main canal and its branches-excepting that of the operculo-mandibular branch-is densely covered by exceedingly minute primitive pores. In many cases they were not visible to the naked eye, but could be clearly distinguished with the aid of a low-power lens. The Operculo-mandibular Branch leaves the main canal a little way in front of the occipital commissure. It passes through the preoperculum and continues along the mandible. At its commencement it gives off numerous fine dermal branches terminating in cluster-pores, the same feature being repeated where it joins with the mandibular portion. There are four large pores on the mandible and numerous small dermal branches and grooves. The branches of the two sides of the head are not connected with each other. 3. T H E C O M M I S S U E E S . - T h e two commissures present in Pimelodus are an imperfect or rudimentary occipital one, whose presence is easily detected by the series of fine dendritic branches passing from it immediately above the angle of the operculum. The second commissure is that in the frontals (PI. XVIII. fig. 4, F.com.). Like the occipital commissure, it gives off numerous fine dendritic branches. It is not so distinct as the frontal commissure in Clarias. Innervation. The distribution of the cranial nerves in Pimelodus resembles very closely the condition described and figured in Clarias magur. The same four nerves are all that enter into relation with the sensory canal system, viz. the trigeminal, facial, glossopharyngeal, and vagus. The branches of the trigeminal innervating sense-organs are:- 1. The ramus ophthalmicus superficialis. 2. The ramus buccalis. 3. The ramus oticus. 1. The ramus ophthcdmicus superficialis has a similar course to this branch in Clarias. Fine branches pass off between the pores 25 to 31 to the sense-organs of the supra-orbital branch of the main canal and also to the frontal commissure. In the most anterior portion the nerve divides into two smaller branches, one passing forwards and around the border of the anterior narial opening, the remaining and smaller branch terminating at pore number 31 (PI. XVIII. fig. 4). 2. The ramus buccalis differs slightly from that found in Clarias in being longer and in the number of its branches and commissures. |
