HALLOVVELI. DAVIS 



6S 



way in which the organ of C'orti breaks under the stress of very intense sound, 

 that the reticular lamina is like a strong rigid plate lying on a more flexible 

 cushion. The rods of Corti serve to pivot its motion around the edge of the bony 

 spiral lamina, near which the foot of the inner rod is attached. The amplitude of 

 movement is greatest near the spiral ligament, well out from the axis of rotation 

 (fig. 5). This rocking of the organ of Corti as a whole while the basilar membrane 

 bulges up and down seems well established as a basic form of movement of the 

 cochlear partition. 



IMBUS 



Fig. 5. Movements of the cochlear partition, based on description by von Bekesy (3). 



The sensory cells of the inner ear, the hair cells, are located in the organ of 

 Corti. Their 'upper' ends are inserted in the reticular lamina to form a contin- 

 uous plate. The bodies of the outer hair cells beneath the lamina lie exposed to 

 the fluid in free spaces within the organ of Corti. Their 'lower' ends are sup- 

 j)orted by cup-like portions of Deiters' cells. The nerve endings of the auditory 

 nerve are closely applied to these lower ends, and lie between the hair cells and 

 their supports. Under the electron microscope (10) the endings appear as 

 structures of some substance, well supplied with mitochondria. The outer hair 

 cells, to which the greatest sensitivity is usually attributed, are thus fixed 

 firmly at their upper and lower ends, but are remarkably free mechanically 

 between these supports. The inner hair cells differ in many details from the 

 outer hair cells, but their general character and situation are similar. 



