The Lateral Line System in Siluroids. 535 



sally from the ganglionic mass and passes through the skull wall just 

 in front of the anterior semicircular canal. Thus it never appears 

 outside the cranium. The 5th organ is supplied by the Glossopharyn- 

 geal which also gives off other sensory branches. 



The 6th sense organ is supplied by the 1st or supratemporal 

 branch of the Vagus. A commissure as in the other Siluroids passes 

 up to join the great recurrent dorsal branch of the Facialis. The 

 last cranial sense organ is supplied by a twig from the Ramus late- 

 ralis vagi. 



Trichomycterus tenuis. (Fig. 5.) 



A small and very young specimen 2^2 cm in length. 



Infraorbital system. The infraorbital system commences 

 just posterior and external to the nasal tentacle at the inner base of 

 which is situated the anterior opening of the nose. The first portion 

 consists of one sense organ with the short tube belonging to it. The 

 condition is really larval only that part of the canal in the immediate 

 neighbourhood of the sense organ being completely closed and two 

 pores being present. Bone has been formed round about the sense 

 organ. 



Behind this first sense organ for a long space no trace of canal 

 or organs could be found. Behind and below the eye occurs the next 

 pore and from it the canal leads upwards and backwards curving 

 posteriorly at the back of the orbit. Directly behind the eye lay the 

 second sense organ enclosed in the postorbital bone. Above it the 

 canal joins the supraorbital, opening at the point of junction by a 

 large pore. 



There are therefore 2 sense organs and 4 (half) pores in this 

 system. 



Supraorbital system. This commences slightly further for- 

 ward than the infraorbital the first pore lying exactly internal to the 

 nasal tentacle and bordering on the anterior uarial aperture. As in 

 the infraorbital line the first sense organ with its tube is separated, 

 though to a less extent, from the following portion. The second (half) 

 pore opens internally to and not far from the posterior narial opening. 

 The sense organ is enclosed in a small ring (»f bone representing the 

 free nasal. 



Beyond the interruption the canal commences again by a pore 

 situated nearly at an equal distance from the edge of the orbit and 



