\>j2 AYERS. [Vol. VI. 



this bundle of fibres, which supplies only the dorsal part of the 

 sac and the sense organ developed there, i.e. the two sense 

 organs which have been described in a previous chapter as 

 occupying places in one of the endolymphatic ducts and in the 

 commissure of the semicircular canals. 



" Unter Beriicksichtigung dieser Umstande glaube ich anneh- 

 men zu durfen, dass auch dem Facialisganglion ein spinaler 

 und ein lateraler Antheil zukommen. 



" Aber die Bildung des letzteren lasst sich von der Gehorblase 

 nicht trennen, beide entstehen durch einen einheitlich zusam- 

 menhangenden Process, der in seiner Gesammtheit der Bildung 

 der ubrigen lateralen Ganglien zu vergleichen ist. Ich glaube, 

 es lasst sich die Auffassung nicht abweisen, dass das Gehorbla- 

 schen in die Kategorie dieser Ganglien gehort. Dann wiirde 

 dem Acusticus die Bedeutung einer spinalen Ganglienwurzel 

 zukommen." From what has been said above it follows that 

 the lower nervous structure connected with the auditory sac 

 furnishes the material for the auditory nerve so-called — that is, 

 all except the accessorius ; and this view I am inclined to believe 

 is the true one. 



From our present knowledge of the development of the ear 

 of Petromyzon as a typical representative of the Cyclostomous 

 vertebrates, we may conclude that the sensory Anlage which 

 lies in the auditory vesicle remains a unit until after the ear is 

 well inclosed. It then buds off from both anterior and posterior 

 ends a sense organ, which at once proceeds in the work of pro- 

 ducing two ampulliferous canals. We know from the adult 

 anatomy that the canals are completely distinct in both Petro- 

 myzon and Myxine. 



The remaining portion of the sense organ Anlage is incom- 

 pletely separated into two parts, but it is uncertain whether 

 this separation had taken place before the canal organs of the 

 anterior and posterior ampullae were budded off. These two 

 sense organs which remain in the utriculo-sacculus are the 

 maculae acusticse utriculi et sacculi, respectively. The division 

 of the parent sense organ leads to a partial division of the com- 

 mon chamber or canal, which is effected by the ingrowth of a 

 median raphe dividing the auditory vesicle into utriculus and 

 sacculus. There are some considerations which I have pre- 

 sented in connection with the discussion of the nerve supply 



