158 MK. F. J. COLE ON THE STRUCTURE AND MORPHOLOGY OF 



anterior edge of the frontal, between the latter and the ligamentous portion of the supra- 

 orbital canal near the mid-dorsal line, to the inner side of the sensory canal, and was 

 traced almost on to the skin and then lost. It most probably supplied the pit organs 

 in that region. 



Coincident with the ligamentous portion of the supra-orbital canal, the ophthalmic 

 trunk separates into its two components, quite obvious with the low power, the lateral 

 constituent being dorsal and the larger of the two. The latter soon afterwards gives off 

 a twig which perforates the posterior edge of the nasal, lies between the latter bone and 

 the supra-orbital canal, and Anally passes obliquely inwards and forwards to supply sense 

 organ 2. • 



The ophthalmic trunk has now completely split up, both components at first lying 

 close together at the posterior extremity of the nasal, ventral to the latter bone and just 

 below the supra-orbital canal. Opposite the second sense organ the two components 

 commence to run alongside again, but do not mingle. Anteriorly the lateral, together 

 with the greater portion of the trigeminal, ophthalmic pass inwards and upwards along 

 the inner face of the nasal, and whilst there a trigeminal twig is given off (S.O.^) which, 

 passing outwards and upwards along the outside face of the nasal, is distributed to the 

 skin in that region. 



Whilst the ophthalmic nerves are passing along the inner face of the nasal the relation 

 between them is for the first time changed, the smaller trigeminal curling round the larger 

 lateral ophthalmic and assuming the dorsal position. Opposite the anterior extremity 

 of sense organ 2 the two components finally separate out and do not for the remainder of 

 their course come into contact again *. The smaller dorsal trigeminal ophthalmic (S.O.^) 

 passes rapidly upwards, dividing into two, is distributed to the skin of the dorsal region of 

 the snout, and, although coursing with the lateral line nerve described in the footnote, is 

 not in any way connected with it. The large ventral lateral ophthalmic, on the other 

 hand, jiasses forwards, perforates the nasal opposite the opening of the second dermal 

 tubide, and terminates in sense organ 1. 



(2) Infra-orbital Canal. 



Buccal Trunk. 



The buccal trunk, leaving the ophthalmic and buccal ganglion, passes downwards and 

 outAvards through the " trigeminal " portion of the trigcmino-facial complex, and whilst 

 passing through this ganglion divides into the nerves (1 and 2 below) which issue from 

 the ganglion at different levels. 



(1) Outer buccal branch. — Issues from the trigeminal portion of the V-VIIth ganglion 

 dorsal and posterior to the second branch. It is smaller than the latter, and gives off', 



* Just at. this region a long nerve from the upper ramus of the inner buccal lateral line nerve passed straight up, 

 crossed the tvro ophthalmic nerves internally, but was not connected with either, curved outwards and round the 

 dorsal edge of the nasal, and finallv passed downwards to innervate a pit organ opposite the anterior extremity ot 

 sense organ 1. This curious nerve is not represented in other fishes, and probably consists of lateral superficial 

 ophthalmic fibres following a buccal course. 



