636 MR FRANK J. COLE ON THE 



(3) Tcleosts (Pollard — Siluroids, e.g., Clarias and Auchenaspis). 



(4) Ganoids (Allis). 



(5) Dipnoi (Pinkus). 



(6) Amphibia (Strong). 



Although it is somewhat anticipating matters, it is necessary that this scheme should 

 be discussed before proceeding to classify and describe the geography of the sensory 

 canals of C/tiuuvra. 



First of all I may quote a passage from a valuable memoir on the cranial nerves of 

 Amphibia by Strong (68), who has in it contributed much to our knowledge of the 

 lateral line system. He says that the innervation of the sensory canals has been found 

 to be essentially the same " in all the forms in which they have been studied and care- 

 fully distinguished"; and further, that though there maybe individual variations, yet 

 " the roots and principal divisions and their arrangement will probably be found to hold 

 good for all." That there is weighty evidence in favour of Strong's statements is obvious 

 to any one who has made a study of the literature of the subject. 



The first thing that will probably strike the reader on glancing at the above scheme, 

 is, why should the vagus take any part in innervating the lateral line system? It is 

 obvious that, with the exclusion from the field of all the cranial nerves except the Vllth 

 and Xth, if the lateralis could only be shown to be connected with the other lateral line 

 nerves, we should then have the whole of the sensory canals supplied by a single system 

 of nerves. The lateralis used to be described as arising from the trunk of the vagus, but 

 this condition has been found to have been an error of observation, and possibly obtains 

 in no single fish. The fact is, as first suggested by Balfour, that the lateralis is quite a 

 distinct nerve from the vagus, and has a ganglion and a separate root in front of the 

 vagal roots, and partly in front of and partly overlapping the root of the glossopharyngeal. 

 This condition I can vouch for in the following forms : Chimsera, Raia, Scyllium, 

 Acanthias, Heptanchus, Lsemargus and Torpedo* 



This fact in itself is both interesting and suggestive, tending, as it does, to show that 

 the lateralis should not be confounded with the vagus. Strong's work, however, com- 

 pletes the case, and further shows that the lateralis must he associated ivith the other 

 lateral line nerves, i.e., considered a component of the Vllth cranial nerve. Strong 

 shows that in Amphibia the superficial ophthalmic of the facial, the buccal, and the 

 hyomandibular (lateral line portion) arise from a common trunk which has its internal 

 origin in the brain from a special nucleus — the " tuber culum acusticum," the only 

 other cranial nerve arising from this nucleus being the lateralis. The lateralis, then, has 

 a totally distinct internal origin from the vagus, and that origin, moreover, is identical with 

 the nucleus giving rise to the other lateral line nerves and to them alone. The lateralis, 



* In this connection it is interesting to note Ewart's description of the root of the lateralis in Leemargus. He says 

 (58, p. 74) : — " The fibres which form the lateralis nerve spring from the side of the medulla, nearly in a line with the 

 middle roots of the facial nerve ; and the anterior fibres lie in front of, and on a higher level than, the roots of the 

 glos8opharyngeu8." Cp. also Stroxg (C8) and Ahlijorn (32). 



