I520 



HUMAN ANATOMY 



upper end terminates in a triangular head, and whose lower extremity expands into the foot 

 resting upon the basilar, membrane. The inner pillar is shorter, more nearly vertical and less 

 curved than the outer ; its head exhibits a single or double concave articular facet for the recep- 

 tion of the corresponding convex surface of the head of the outer rod. The cuticular substance 

 of both pillars adjoining the articular surfaces is distinguished by a circumscribed, seemingly 

 hornogeneous oval area of different nature. The upper straight border of the head of each pil- 

 lar is prolonged outwardly into a thin process or head-plate, that of the inner lying uppermost 

 and covering over the head and inner part of the plate of the outer pillar. The head-plate of the 

 latter is longer and projects beyond the termination of the plate of the inner rod as \he phalan- 

 geal process, which unites with the adjacent phalanges of the cells of Deiters to form the metn- 

 brana reticularis. The inner pillars of Corti are more numerous, but narrower than the outer 

 elements, from which arrangement it follows that the broader outer rods articulate with two and 

 sometimes three of the inner pillars, the number of the latter in man being estimated by Retzius 

 at 5600, as against 3850 of the outer rods. 



Immediately medial to the arch of Corti, resting upon the inner rods, a single row of spe- 

 cialized epithelial elements extends as the inner auditory or hair-cells. These elements, little 

 more than half the thickness of the epithelial layer in length, possess a columnar body contain- 

 ing an oval nucleus. The outer somewhat constricted end of each hair-cell is limited by a 



Outer hair-, 

 cells 

 Hensen's cells 



Cells of 

 Claudius 



Cells of Deiters 



Fig. 1273. 



Nuels space Inner hair-cells 



Membrana tectoria 



Section showing details of Corti's organ from human cochlea ; owing to slight obliquity of section, width is some- 

 what exaggerated. ■; 375. Drawn from preparation made by Dr. Ralph Butler. 



sharply defined cuticular zone, from the free surface of which project, in man, some twenty-five 

 rods or hairs. The inner hair-cells are less numerous (according to Retzius about 3500), as well 

 as shorter and broader, than the corresponding outer elements. Their relation to the inner rods 

 of Corti is such, that to every three rods two hair-cells are applied. The inner sustentacular 

 cells extend throughout the thickness of the epithelial layer and exhibit a slightly imbricated 

 arrangement as they pass over the sides of Corti's organ to become continuous with the lower 

 cells of the sulcus spiralis. 



The cells covering the basilar membrane from the outer pillar to the basilar crest comprise 

 three groups: (a) those composing the outer part of Corti's organ, including the outer hair- 

 cells and cells of Deiters ; {d) the outer supporting cells, or cells of Hensen ; (r) and the low 

 cuboidal elements, the cells of Claudius, investing the outermost part of the basilar membrane. 



The outer auditory or hair-cells are about five times more numerous (approximately 18,000 

 according to VValdeyer) than the corresponding inner elements, and in man and apes are dis- 

 posed in three or four rows. They altertiate with the peculiar end-plates or "phalanges" of 

 Deiters' cells, which separate the ends of the hair-cells and join to form a cuticular mesh-work, the 

 tnenihrana reticularis, through the openings of which the hair-cells reach the free surface. The 

 inner row of these cells lies directly upon the outer rods of Corti, so placed that each cell, as a 

 rule, rests upon two rods. The cells of the second row, however, are so disposed that each cell 

 lies opjiosite a single rod, whilst the third layer repeats the arrangement of the first. In conse- 

 quence of this grouping, these eleinents, in conjunction with the " phalanges," appear in surface 

 views like a checker-board mosaic, in which the oval free ends of the auditory cells are included 

 between the peculiar compressed and indented octagonal areas of the end-plates of Deiters" cells 



