THE SENSE OF HEAKING 



215 



Zona, pecbisiafa 

 rf 



. Zona. otjrcuatci. 



rods of Corti are attached, and 

 the zona pectinata, extending 

 from the base of the outer rods 

 to the spiral ligament (Fig. 83). 

 The latter zone is somewhat 

 thicker and more fibrous. The 

 basilar membrane, as a whole, is 

 composed of a homogeneous sub- 

 stance, nucleated here and there, 

 with straight elastic fibres run- 

 ning from the spiral lamina to 

 the spiral ligament embedded in 

 it, so that from the surface it 

 appears to be distinctly striated, 

 and in section the fibres are seen 

 as colourless dots in the homo- 



i '. \, feet if i 

 * 







for n,w&. 



Fio. 84. Tangential section across the zona 

 * pectinata of basilar membrane of Guinea-pig. 

 Highly magnified. (Schwalbe.) 



geneous ground-substance (Fig. 

 84). 



On the upper surface of the 

 basilar membrane is the com- 

 plicated epithelial formation 

 known as the organ of Corti, the 

 true peripheral apparatus which 

 transmits the auditory excitations 

 to the sensoriuin (Fig. 85). The 

 central part of this apparatus 

 consists of two sets of stiff rod- 

 like bodies standing some little 

 distance apart on the basilar 

 membrane, and inclined towards 

 each other so that they come 

 into contact above. These are 

 the rods of Corti, each pair of 

 which forms an irregular pointed 

 arch, and the double row of in- 

 clined columns forms a tunnel 

 along the whole extent of the 

 cochlear canal. 



On the inner side of the inner 

 series of rods is a row of epi- 



FIG. 83. Basilar membrane and limbua viewed fU i: Q i O all anvinrmnfprl hv a 

 from above. Magnified. (G. Retzius.) tnelial CCllS SUlinOlinteU Py a 



