are 



CRANIAL NERVES OF CHIMyERA MONSTROSA. 635 



C. The Classification of Sensory Canals. 

 The sensory canals of fishes and amphibia may be divided into four groups, which 



(1) The lateral canal running from the tip of the tail forwards at the side of the 



body. This, just posterior to the orbit, divides into 



(2) The supra-orbital canal, coursing over the eye, and 



(3) The infra-orbital canal, situated under the eye. 



(4) The hyomandibular or operculo-mandibular canal is a branch of the infra-orbital, 



and runs outwards at rio;ht angles from it. 



Until comparatively recently, the most conflicting views have been held as to the 

 innervation of these canals, and one is constantly encountering statements to the effect 

 that the Vth cranial nerve does a great, if not the greater, part of the work. There 

 can be no doubt therefore, in discovering the buccal nerve to be a branch of the Vllth, 

 and not of the Vth, as had previously been believed, and further, in firmly establishing 

 the existence of an ophthalmicus superficialis portio facialis, that Marshall and Spencer 

 laid the foundation upon which the knowledge we now possess of the lateral line system 

 has since been largely built. 



The Vth cranial nerve, then, being excluded from the field, the way was prepared 

 for the elucidation of the following scheme, which is founded upon the results obtained 

 by those investigators who have made a careful and special investigation of the lateral 

 line system : — 



(1) The lateral canal and occipital or supra-temporal commissure are innervated 



by the lateralis division of the vagus. 



(2) The supra-orbital canal is innervated by the superficial ophthalmic division of 



the facial. 



(3) The infra-orbital canal is innervated by the buccal and otic divisions of the 



facial. 



(4) The hyomandibular or operculo-mandibular canal is innervated by the external 



mandibular division of the facial. 



It is thus seen that the innervation of the lateral line system comes from the 

 Vllth and Xth nerves only, but there are apparent exceptions which will be discussed 

 later on. 



By confining ourselves to the researches of those who have paid special attention to 

 the lateral line system, and have made a careful examination of the nerves, we find that 

 the above scheme applies to all the classes of animals in which the system is either a 

 permanent or temporary characteristic, e.g. : — 



(1) Holocephali (present communication). 



(2) Elasmobranchs (Ewart). 



