Johnston, The Brain of Petroinyzon. 53 



VII, Miss Alcock mentions only one root, and has overlooked 

 the communis root. Failure to recognize this as a separate 

 root gives an erroneous conception of the nature of the VII-X 

 anastomosis and hence of the nature of the lateral line nerve. 



Cole ('98) in criticizing this paper questions whether all 

 the organs described by Miss Alcock are lateral line organs. 

 The facts set forth in the present paper settle this question in 

 Miss Alcock's favor so far as the identification of lateral line 

 organs is concerned. It must be said that Cole was much more 

 severe in his criticism than the known facts at the time war- 

 ranted and that he took the wrong course in doubting the exist- 

 ence of lateral line organs and components where Miss Alcock 

 had seen them. 



Cole ('98 a) also questions the interpretation of the ramus 

 lateralis vagi as a lateral line nerve, and this point requires some- 

 what fuller attention. Strong ('95, p. 199), after quoting 

 Ahlborn's description of the nerve roots in Petromyzon, says : 

 "The first fact that impresses one in this arrangement is that 

 the first set of roots from the Acusticus region do not form the 

 N. lateralis, but the R. branchialis. Furthermore, the N. lat- 

 eralis is formed partly by a recurrent branch of the Facialis 

 passing around outside the auditory capsule — a thing which 

 does not occur in the N. lateralis in higher forms. Again on 

 comparing the course of the N. lateralis with the arrangement 

 of the pits, it is evident that only a small proportion of them 

 would be innervated by this nerve, which has a position near the 

 mid-dorsal line. When these facts are considered — especially the 

 non-derivation of this nerve from the Acusticus center, thus 

 differing from the origin so universal for all other forms — it must 

 be regarded as very probable that this nerve does not represent 

 the N. lateralis vagi of higher forms. . . What it docs rep- 

 resent is probably the R. lateralis trigemini, so-called, of Tcle- 

 osts — a nerve which is formed principally, as we have seen, by 

 a recurrent branch of the Facialis, derived from th^- lobus tri- 

 gemini [i. e., of Teleosts, — the cephalic part of the lobus vagi 

 or fasciculus communis], and which is reenforced by a branch 

 from the vagus. It would then much more probably innervate 



