THE CRANIAL NERVES AND LATERAL SENSE ORGANS OF FISHES. 175 



canal organs or end buds. Tliey have not, however, been traced caudad more than a few 

 segments into the trunk. They clearly correspond to the superficial, or accessory 

 " lateral line," nerves of the Gadoids." Here the lateral line character of the accessory 

 lateral is out of the question, but I am astonished to find that its fibres all belong to the 

 fasciculus communis system, since this, as we know from Strong (1895, 204, p. 182), 

 consists in Amphibia exclusively or almost exclusively of visceral fibres *. It is ti-ue, as 

 I have previously pointed out, that other recent aiithors have made similar statements, 

 and Strong himself has been somewhat misrepresented in the matter. The somatic sensory 

 fibres cannot be considered to belong to the fasciculus communis system, unless we are to 

 be guilty of the sophism of extending the definition of this system in order to admit 

 them. The authors in question disassociate viscn-al sensory from visceral motor fibres, 

 and then unphilosophically proceed to associate somatic with splanchnic fibres and call 

 the result by a name which was oi'iginally applied to a system of viscei'al sensory nerves. 

 The system adopted by Strong and Herrick of ascertaining both the internal origin and 

 the peripheral distribution of the cranial nerve components is the only one by which to 

 attain results of any value, and we must accordingly await further investigation on these 

 lines as to the nature of the fasciculus communis system in fishes. In the meantime 

 we may or may not choose to believe in the conversion of splanchnic into somatic 

 fibres. 



It is hence perfectly clear that the accessory lateral nerves of fishes consist, as has been 

 proved microscopically, of somatic sensory fibres. And their peripheral distribution has 

 also been clearly described and figured by many autliors, such as Swan and Stannius. 

 Their origin, however, excepting the doubtful accessory lateral described by Haller, has 

 hardly been investigated at all, and the utmost we know is that in many fishes it is 

 formed by roots from at least two cranial nerves. I therefore made a careful investigation 

 of the origin of the system in Gadus virens, with the results detailed below. 



In Gadus, as is well known, the accessory lateral nerve arises by two roots — a large 

 stout anterior root, and a much smaller posterior root. An anatomical and microscopical 

 examination of these two roots reveals the following facts : — 



Anterior or Trlgemino-facial root {anatomical). — Arises from the trigemino-facial 

 ganglion by two rootlets — a larger and a smaller. Owing to the fact that these arise 

 from the complex just as the latter is passing through and leaving the skull, and as the 

 nerves are here closely invested by a tough membrane very difficult to dissect off, the 

 origin of the rootlets is difficult to ascertain. Tlie larger one, however, was connected 

 by several bundles with the base of the hyomandibular trunk, and the smaller one with 

 the maxillo-mandibular trunk. The actual origin of the fibres I was unable to 

 determine by dissection. The two rootlets embrace the trigemino-facial ganglion 

 in much the same way as the rootlets of the posterior root embrace the trunk of the 

 vagus. 



Anterior root [microscopical). — Both the rootlets arise from the trigemino-facial complex 

 intracranially, or rather as the complex is passing through the pro-otic notch. The 

 larger rootlet arises by several bundles from tlie most ventral fibres of the hyomandibular 



* Cp. also p]). I9.T-6. 



