284 MB. W. E. COLLUfGE ON THE [Apr. 2, 



The Stth-orbital Branch is the lateral division of the main canal. 

 It is conducted around and helow 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 bj^ 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 Opercido-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 com- 

 mencement 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 nimierous small dennal branches and grooves. The 

 branches of the two sides of the head are not connected with each 

 other. 



3. The Commissuees. — The two commissures present in Pime- 

 lodus 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 commissvu'e 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 superficiaUs. 



2. The ramus buccalis. 



3. The ramus oticus. 



1. TJie ramus ophthalmicus superficiaUs has a similar course to 

 this branch in Clarias. Tine 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, 



