INTERNAL EAR 609 



them, a very dose mechanical model of the cochlea would have been 

 obtained. The peculiar shape of the cochlea would therefore appear to be 

 explained on the supposition that it is compensated against accelerations 

 and gravity. 



THE ORGAN OF CORTI. The end-organ of the auditory nerve 

 is represented by the organ of Corti, which rests on the basilar membrane 

 (Fig. 309). It consists of a double row of stiff cells, the inner and outer rods 



B.M 



FIG. 309. Section through the end-organ of the auditory'^ nerve in the cochlea 



(organ of Corti). 



BM, basilar membrane ; c, canal of Corti ; nc, rods of Corti ; IH and OH, inner 

 and outer hair-cells ; sc, sustentacular cells ; An, auditory nerve ; mt, membrana 

 tectoria. 



of Corti, which run throughout the whole length of the scala media and are 

 surrounded by sense epithelium, the hair-cells. On the inner side of the rods 

 of Corti there is a single row, on the outer side three rows of hair-cells. Between 

 the hair-cells are the sustentacular cells, or cells of Deiters, the peripheral 

 processes from which join together so as to form a reticulate membrane 

 over the hair-cells, the hairs themselves projecting through orifices in the 

 membrane. Resting on* the upper surface of the membrana reticularis is 

 the membrana tectoria. To this membrane is often ascribed a damping 

 effect on the vibrations of the structures below. Any movement of the basilar 

 membrane would be transmitted to the rods of Corti, and by these to the 

 overlying hair-cells. With every vibration these would move in the line 

 of their long axis so that their hairs would move up and down and possibly 

 strike against the under surface of the membrana tectoria. 



Other views have however been advanced as to the way in which the hair 

 cells become stimulated. Thus Wrightson states that there is a to and fro 

 movement between the hair- cells and the membrana tectoria so that the 

 hairs are bent first to one side and then to the other. Keith suggests on the 

 other hand that the hairs are embedded in the membrana tectoria and that 

 the stimuli are set up by the pulling and bending of the hairs which must 

 occur when the basilar membrane is moved. Further research is required 

 to elucidate this point. The fibres of the auditory nerve pass up through 

 the column of the cochlea, through the bipolar ganglion cells which form the 

 spiral ganglion, and then out along grooves in the spiral lamina to end in 

 arborisations, partly in the inner hair-cells and partly among the outer hair- 

 cells. 



NUTRITION OF COCHLEA. The organ of Corti and the surrounding struc- 

 tures appear to obtain nutrition from three different sources. (1) Arterial twigs pass 



39 



