130 A VERS. [Vol. VI. 



Although the ontogenetic evidence on this subject is not 

 by any means as complete as the importance of the subject 

 demands, since no special attention has been paid to the rela- 

 tion of the facial nerve to the auditory invagination, except by 

 Kupffer, nor to the relations of the rest of the nerve supply of 

 the ear at this stage of growth, which is usually considered the 

 whole auditory nerve, there are certain facts which point to the 

 conclusion that the auditory organ has arisen from the trans- 

 formation of two originally distinct sense organs, which have 

 been sunk below the surface in a common pit. 



In order to adequately understand the relation of the auditory 

 canal complex to its nerve supply, it will be necessary to exam- 

 ine three nerves usually classed as distinct cranial nerves, with 

 respect to their central origin, their ganglionic connections, and 

 their peripheral distribution ; viz. the VII or facial, VIII or 

 auditory, and the IX or glossopharyngeal. When we examine 

 the knowledge of the external origin and distribution of these 

 three nerves in the light of recent work, we find that so far as 

 the auditory nerve is concerned the distinctly separate external 

 relations are but reflections of central relations equally distinct 

 and separate. 



The innervation of the auditory sense organs in the Cyclo- 

 stome fishes is manifestly a matter of importance, if, as I believe, 

 the known representatives of the group are to be regarded as 

 retaining, on the whole, ancestral conditions of structure. 



In Myxine and Petromyzon we find the N. acusticus divided 

 into two very distinct rami, — the anterior and posterior or 

 utricular and saccular rami, respectively, — whose peripheral dis- 

 tribution is strictly confined to the chamber to which it runs. 

 This is not only true of the Cyclostomes, but, with very slight 

 changes, is true of all the Gnathostomata, and is consequently 

 a fundamental fact whose full significance we are not yet in a 

 position to fully appreciate. 



According to Retzius, in the Hagfish [Myxine ghitinosd) the 

 auditory nerve arises from the brain, posterior to the origin of 

 the V with two ganglion-bearing roots on either side. These 

 ganglia are flattened bodies which lie close together, but are 

 entirely separate structures. They give off several branches to 

 the sense organs of the ear. From the larger, anterior ganglion 

 two branches pass off to the crista ampullae anterioris and one 



