126 



GERMINATION 



I say " what is called," because it is in reality two nerves, 

 and although both form part of the same apparatus only 

 one of them need be taken into account in connection with 

 quality of sound, and that — probably the true nerve of 

 hearing — is the cochlear nerve. 



Membranous I/Abyrinth of a Five Months' Foetus, 

 viewed from its postero-medial aspect. [Retzius.) 

 a, Cochlear nerve ; b, Nervus facialis ; c, Vestibiilar nerve ; d. Macula 

 acustica sacculi ; e, macula acustica utriculi ; /, Ampulla of superior 

 duct ; g, Sinus superior ; h, Ligamentum spirale ; i, Membrana basilaris ; 

 7, Branches of cochlear nerve to organon spirale ; k. Branch of cochlear 

 nerve to ampulla of posterior duct ; /, ductus reuniens ; m, Ductus 

 endolymphaticus ; n. Sinus inferior ; o. Ampulla of posterior duct ; 

 p, q, r. Semi-circular canals. 



Cunningham, in his Text Book of Anatomy, says : " The 

 Nervus Acusticus . . . enters the brain at the inferior 

 border of the pons. Its fibres spring from bipolar ganglionic 

 cells in the immediate neighbourhood of the labyrinth. 

 One group Jbf these forms the spiral ganglion, the peripheral 

 branches of which are distributed to the organ of Corti in 

 the cochlea : another group constitutes the vestibular 

 ganglion which distributes fibres to the ampullae of the 

 semi-circular ducts and the utricle. Although the central 

 processes of the cells of these two ganglia accompany one 

 another and are known collectively as the Acoustic Nerve, 

 they really remain distinct throughout, in their mode of ter- 

 mination in the brain as well as in their peripheral 

 distribution." 



