THE INTERNAL EAR. 



49 I 



inner pillar, is a depression into which fits the head of the outer 

 pillar. The latter also extends outward in the shape of a phalan- 

 geal plate, with a thinner process, the phalangeal process, at its end. 

 The phalangeal plate and process lie under the head-plate of the 

 inner pillar, the process extending a little beyond this, forming an 

 acute angle with the head of the outer pillar. At the inner side 

 of the head of the outer pillar is a convex articular surface, with 

 which, as a rule, two, and occasionally even three, articular sur- 

 faces of the inner pillars come in contact. The outer and inner 

 pillars appear to possess an indistinct longitudinal striation, and 

 their basilar plates are continuous with the extremely fine cuticula 

 covering the basilar membrane. The inner margins of the basilar 

 plates belonging to the inner pillars border on the foramina ner- 

 vosa ; while the outer margins of the basilar plates belonging to 

 the outer pillars come in contact with the basal end of the inner- 

 most row of the cells of Deiters in the outer region of Corti's 

 organ. The protoplasmic portions of the pillar cells, constituting 

 what are known as basal cells, lie against the basilar plates of the 

 corresponding pillars, i, e., on the basilar membrane, and partly 

 cover the bodies of the pillars, especially the surfaces toward the 

 tunnel. 



In order to comprehend the relative position of the inner audi- 

 tory cells to the inner pillars, it may be stated that one auditory 

 cell rests upon every two inner pillars. 



The outer region of Corti's organ is joined directly to the outer 

 pillar -cells, and consists of four rows of auditory cells alternating 

 with an equal number of sustentacular cells or Deiters's cells. 

 Following these structures and in contact with them are the outer- 

 most sustentacular cells, known as Hensen's cells. 



The outer auditory cells have a structure similar to that of the 

 inner auditory cells, but possess a more slender body. They do 

 not extend as far as the basilar membrane, but end at a distance 

 from the latter equal to about double their own length. The cutic- 

 ular zone of each outer auditory cell likewise assumes the form of 

 an ellipse, with its long axis pointing radially. The surface of this 

 zone also is provided with about twenty stiff auditory hairs, 

 arranged in the form of a decidedly convex arch, the convexity of 

 which points outward. At a short distance from the cuticular zone 

 of each outer auditoiy cell is a peculiar round body, found only in 

 these cells, the significance of which is unknown. 



Deiters's cells rest on the basilar membrane, and in shape resem- 

 ble a flask with a narrow neck, known as the phalangeal process, 

 the latter lying between the auditory cells. The nuclei of Deiters's 

 cells lie in the upper parts of the thickened basal portions of these 

 cells. 



With each Deiters's cell there is associated a cuticular structure, 

 which extends along the surface of each cell in the form of a thin 



