THE EAR OF MAN. 2I9 



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 ductus endolymphaticus is supplied on its 

 anterior face by a branch of the utricular nerve, while 

 its distal end, in some fishes, opens into a canal con- 

 taining sense-organs innervated by the glossopharyngeal 

 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 preauditory 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 phylogenetically accounted for, and at the same 

 time the early ontogenetic changes in the auditory 

 vesicle receive their explanation. 



The two sense-organs, the maculae acusticae 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 



