The Lateral Line System in Siluroids. 529 



Ramus buccalis, the first and second by one twig, the rest by sepa- 

 rate twigs which as in the case of organs four and five separate very 

 early from the buccalis and take long indei)endent courses. The buc- 

 calis and ophthalmicus superficialis unite to form one trunk some way 

 from the ganglion, into which they pass. The ganglionic mass belong- 

 ing to the Trigeminus and Facial nerves lies inside the skull beside 

 the brain but the ophthalmicus superficialis and buccalis lie outside 

 the cranium. The sixth sense organ of the supraorbital system is 

 supplied by a nerve which runs entirely intracranially till it pierces 

 the dermal bone to reach the sense organ. It arises dorsally from 

 the ganglion, not from the ophthalmicus superficialis and may well 

 be considered in Clarias an independent nerve. The sixth organ of 

 the main canal is supplied by the Ramus oticus which arises with 

 the common trunk of the buccalis and ophthalmicus superficialis. It 

 runs upwards intracranially and reaching the dermal bone turns sharply 

 back over a sensory nerve, which runs out transversely, and proceeds 

 to the sense organ. 



The Ramus oticus gives oti" also a sensory branch which does not 

 l)ass to any organ of the mucous canal system. The seventh organ 

 of the main canal is supplied by the Glossopharyngeus. This nerve 

 also gives ofi' another sensory branch to the top of the skull. The 

 root of this nerve closely accompanies the Vagus. 



The eighth organ is supplied by the first branch of the Ramus 

 lateralis vagi, which also passes dorsally towards the middle line as 

 the Ramus supratemporalis. This joins the recurrent nerve of the 

 Facial. 



The ganglion of the Ramus lateralis vagi is situated intracranially 

 and the root of the nerve arises far forward on the medulla from the 

 same region as the mucous branch of the Facial nerve. 



A large branch of the Faciahs (Fig. la;) arises dorsally from the 

 fused Facial and Trigeminal ganglia and proceeds upwards towards the 

 roof of the skull. From the same region of the ganglion arises also 

 a nerve (Fig. ly) which runs forward intracranially and penetrates the 

 dermal bone passing beneath the supraorbital mucous canal between or- 

 gans 4 and 5. It supplies the roof of the skull external to the sense 

 organs 3, 4 and 5 of the supraorbital system. The branch x passes 

 enclosed within the frontal and postfrontal bones transversely outwards 

 crossing beneath the Ramus oticus. (Corresponding nerves are pre- 

 sent in some Teleostei and Folypierus.) From a posterior dorsally 

 placed ganglionic extension arises the great Ramus dorsalis recurrens 



