No. I.] THE VERTEBRATE EAR. 129 



embryologists and comparative anatomists are familiar with the 

 very intimate relation existing between the auditory and facial 

 nerves, and many are inclined to consider the two, parts of a 

 single cranial nerve. The majority of those holding such 

 ideas probably favor the view that the auditory nerve is the 

 dorsal sensory root of the nerve of which the facial is the ven- 

 tral motor root. 



No final conclusions can be drawn from the evidence disclosed 

 by the investigations in this field alone. There are a few facts 

 which stand out with clearness, however, and they tend to show 

 how very intimate the connection is between the VII, VIII, 

 and IX nerves. 



I have shown above that the auditory vesicle is marked off 

 into anterior and posterior portions very early in life ; but we 

 do not know of any facts which lead to the conclusion that the 

 vertebrate ear was ever functional in the vesicular stage with 

 a single sense organ. As soon as we can recognize the audi- 

 tory nerve, it is made up of two diverging portions which are 

 never related in their central connections, but arise from widely 

 separated tracts. Each nerve root is provided with an inde- 

 pendent ganglion applied to the two divisions of the auditory 

 vesicle which show two sense organs, the maculae utriculi and 

 sacculi. There is no extensive anastomosis between the two 

 roots of the auditory nerve. 



They arise from separate tracts ; they run in separate paths ; 

 they end in separate organs. Could there possibly be any 

 completer evidence that these two nerves are distinct structures, 

 and that the parts of the ear which they supply are simply asso- 

 ciated organs of different pedigrees .-* 



This conclusion is based on present anatomical conditions, and 

 does not speculate on possible ancestral relations of the nerves. 



If, on the one hand, the two roots of the auditory do "not 

 anastomose with each other, they do, on the other hand, enter 

 into anastomosis, or more truly, perhaps, they retain their primi- 

 tive anastomoses, with their parent branches. The anterior 

 root or utricular nerve anostomoses with the facial nerve, while 

 the posterior branch either runs entirely independent to its 

 peripheral territory or anastomoses in some few Elasmobranch 

 forms with the so-called anterior root of the ninth or glosso- 

 pharyngeal nerve. 



