304 



THE NERVOUS SYSTEM 



above, part of the membranous labyrinth and is filled with 

 endolymph. 



Upon the basilar membrane are the two rods of Corti, 

 which lean together, so that with the part of the basilar 

 membrane between them they form a tunnel extending 

 all the way up the cochlea. Leaning against the inner 

 rod is a row of hair-cells, and external to the outer rod 



LAMINA 

 SPIRALIS 



ME.MBIV1NEOF 

 R.EI55NEFL 



MEMBRANA-j 

 TECTORIA 



5CALA TYMPANI 



SCALA MEDIA 



SCf\\J\ 

 VLSTIBULI 



SPIRAL GANGLION 



AUDITORY NERVE 

 'ORGAN OF CORTI 

 Fig. 52. — Diagrammatic vertical section through cochlea. 



BASEMENT 

 MEMBRANE 



are several rows of the same, separated by sustentacular 

 cells. The hair-cells are the peripheral end-organs of the 

 auditory nerve, filaments of which reach them by passmg 

 up the modiolus and along the base of the spiral lamina. 

 From the spiral lamina a projection known as the mem- 

 brana tectoria overhangs the hair-cells so that its under 

 surface either just touches or just fails to touch the ends 

 of the hairs. 



When the stapes drives the fenestra ovahs inwards the 

 increase in pressure is communicated to the perilymph in 



