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AYERS. [Vol. VI. 



the cells of origin in the ear to the so-called nuclei in the 

 brain), one lying in close connection with the facial nuclei, the 

 other intimately related with the glossopharyngeal nucleus. 



2. In all eared vertebrates the so-called auditory nerve is 

 composed of two distinct roots — an anterior and a posterior — 

 which supply the anterior and posterior chambers respectively. 



3. In all these forms the anterior root is external to the 

 brain, united with the facial nerve. 



4. In some fishes the nerve to the posterior ampulla is 

 derived from the glossopharyngeal nerve, between which nerve 

 and the posterior root of the auditory there exists, however, a 

 more proximal connection. 



5. The auditory vesicle is always developed between the 

 facial and glossopharyngeal nerve roots. 



6. The endolymphatic ducts are supplied on their mesial 

 faces by branches of the utricular and saccular nerves, while 

 the distal end of the saccular duct, in some fishes, opens into a 

 canal containing sense organs innervated by the glossopharyn- 

 geal nerve. 



7. The so-called eighth cranial or the auditory nerve must 

 have arisen from branches of two distinct cranial nerves, and 

 is not homodynamous with such cranial nerves as the fifth or 

 tenth, as we now understand them. This is true {a) because 

 the auditory sense organs thus supplied were primarily only a 

 portion of the canal sense organs innervated by the original 

 nerves of the pre-auditory condition of these sense organs ; 

 {b) because the auditory nerve is clearly not a complete nerve, 

 and is not even equivalent to a dorsal root of a cranial nerve, 

 for its two divisions are probably merely branches of the dorsal 

 roots of the seventh and ninth nerves, since they draw off only 

 a portion of the sensory fibres from these two nerves. 



The primitive division of the auditory chamber and its nerve 

 supply into two so sharply marked portions is thus phylogeneti- 

 cally accounted for, and at the same time the early ontogenetic 

 changes in the auditory vesicle receive their explanation. 



The two sense organs, the maculae acusticse of the utriculus 

 and sacculus, are thus derived from two organs terminating two 

 separate canal systems which had, as they may still be seen in 

 Amia, become confluent on the surface of the body midway 

 between the roots of the facial and glossopharyngeal nerves as 



