G74 MR FRANK J. COLE ON THE 



internal mandibular, which latter nerve she agrees with me in regarding as essentially 

 the post-branchial division of the facial, and Strong's nerve is certainly not a post- 

 branchial nerve. I have no doubt from Miss Platt's description and figure that her 

 ' external palatine ' is the homologue of the prse-spiracular of fishes, and therefore of 

 the chorda tympani of mammals. 



Summary. 



1. The present communication contains practically the first account of the nerves of 

 any Holocephalous fish. 



2. Sensory canals in general may be said to consist of four divisions — lateral, 

 supra-orbital, infra-orbital, and hyomandibular (operculo-mandibular). These divisions 

 have been found to be innervated from the Vllth and Xth nerves only in all forms 

 carefully examined, and any exceptions to this rule will probably break down, as many 

 have already broken down, on investigation. Eepresentatives of all the five classes of 

 fishes, and of the Amphibia, have been described as falling in with the above scheme. 



3. The lateral line divisions of the Vllth, IXth, and Xth nerves of Fishes and 

 Amphibia must be considered as forming a single and perfectly independent system of 

 nerves, developed in connection with a special sensory system, and associated mostly 

 with the facial nerve. It is therefore erroneous to suppose that the sense organs of the 

 lateral line have any ' segmental ' value. 



4. Fibres from one cranial nerve may accompany the branches of another. 



5. The canals of the lateral line system must be classified according to their innerva- 

 tion, and not according to the relative position they may occupy to other parts of the 

 body. 



6. An accurate definition of a ' segmental ' nerve is perhaps not at present possible. 

 The cranial nerves may not have any ' segmental ' value in the accepted sense of the 

 term. 



7. The lateral line system of Fishes and Amphibia is innervated as follows : lateral 

 canal and occipital commissure = lateralis (vagus) ; supra-orbital canal = superficial 

 ophthalmic (facial) ; infra-orbital canal = buccal + otic (facial) ; hyomandibular or 

 operculo-mandibular canal = external mandibular (facial). The association of the lateralis 

 with the vagus must have been secondarily acquired, and doubtless all the lateral line 

 nerves arose primitively by a single root from the ' tuberculum acusticum.' 



8. The chorda tympani of Mammals is represented in Fishes and larval Amphibia 

 by the pras-spiracular or prse-branchial division of the facial. 



9. The roots of the Vth and Vllth, and the post-spiracular hyomandibular trunk, 

 have in the typical Selachian the composition stated on pp. 662-3. 



1 0. The superficial ophthalmic and buccal divisions at least of the lateral line system 

 must be regarded as having arisen by the splitting of a single trunk, and the supra- 

 orbital and infra-orbital canals must also have arisen by a similar process. 



