THE CRANIAL NERVES AND LATERAL SENSE ORGANS OF FISHES. 165 



Supra-temporal branch. — This branch arises from a clump of ganglion cells (which also 

 extend into its proxixnal portion) from the lateralis immediately the latter emerges from 

 the skull. It curves round the auditory capsule, and passes at first in a vertical plane 

 outwards and then upwards. The first bi-anch to be given off is a small posterior one. 

 It arises from the ventro-external portion of the supra-temporal a little distal to the 

 ganglion cells, and passes straight backwards, pierces supra-temporal 4, and supplies the 

 fourth sense organ of the lateral or body canal. It also gives off two branches : first, 

 a somewhat obvious one, which passed forwards and somewhat downwards, bifurcated, 

 and was lost on the skin (this was separated off near the origin of the posterior branch 

 of the supra-temporal) ; second, a bundle of fibres which was given off as the parent 

 nerve approached the fourth sense organ, and which passed backwards and was also lost 

 on the skin. Neither of these nerves ended in the vicinity of pit organs. 



The larger part of the supra-temporal now takes an upward and forward turn, but 

 before reaciiing the lateral canal divides into two — a dorsal and an anterior division. 

 The former {U) passes upwards and crosses the lateral canal internally and posterior to the 

 entry of the supra-temporal canal, ^vhilst the latter (i*) passes at first straight forwards 

 just below the lateral canal. JO'' soon divides into two branches. The lower of these 

 perforates the second supra-temporal and innervates sense organ 2 of the supra-temporal 

 canal; the upper courses upwards and forwards, perforates the first sujira-temjioral, and 

 supplies sense organ 1 of the line. L* passes forwards and slightly upwards, passes in 

 between the opposed horizontal edges of supra-temporals 2 and 3, and thus reaches 

 sense organ 3 of tlie lateral canal. Just as it passes in between these ossicles it gives 

 off a twig which jiassed forwards and was lost on the skin above the lateral canal. Here 

 also there was an absence of any pit organs. It seems to me probable that this branch, 

 as well as the similar ones first described, arc composed of fibres of the vagus which 

 have accompanied the supra-temporal nerve and its branches *. 



The main trunk of the lateralis, after giving off the supra-temporal branch, passes 

 downwards, outwards, and backwards, and in the sections is seen to be situated between 

 the dorsal border of the pseudobranch and the kidney. As it passes backwards it divides 

 to form two conspicuous nerves, one of wliich is distinctly smaller than the other. The 

 smaller division passes upwards and outwards over the top of the pseudobranch, and then 

 straight backwards, but before doing the latter gives off' externally a largish nerve, which 

 itself separated off a very small twig and then passed straight downwards in the inner 

 wall of the branchial chamber. I was unable to trace this branch. The parent nerve, 

 ho\\'cver, then coursed outwards and upwards, pierced tlie first lateral line ossicle, and 

 innervated sense organ 5 of the lateral or body canal. 



After giving rise to the nerve above described the smaller or dorsal ramus of the 

 lateralis trunk continues to pass upwards and backwards approaching the lateralis canal, 

 and as it does so it sends off a branch dorsally which passes first upwards and then 

 forwards for some little distance and markedly dorsal to tlie lateral canal. It was finally 

 lost on the skin. Almost immediately afterwards another small branch was given oft', 



* Cp. particularly description of posterior root of accessory lateral nerve, p, 176. 



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