THE ORGAN OF HEARING. 303 



triangular nucleated thickening at the base directed towards 

 the cavity of the tunnel. 



Each pillar possesses a slender slightly-S-shaped longitudinally- 

 striated body, whose upper end terminates in the triangular head, 

 and whose lower extremity expands into the foot resting upon the 

 basilar membrane. The inner pillar is shorter, more perpendicular, 

 and less curved than the outer ; its head exhibits a single or double 

 concave articular facet for the reception of the corresponding 

 convex surface of the head of the outer rod. The cuticular sub- 

 stance of both pillars adjoining the articular surfaces is distinguished 

 by a circumscribed seemingly homogeneous oval area of different 

 nature. The upper straight border of the head of both pillars is 

 prolonged outwardly into a thin process or head-plate, that of the 

 inner rod 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 



Diagrammatic view of Corti's organ : A , inner pillars of Corti (with head-plates a) ; B, outer pillars ; 

 C, tunnel of Corti ; D, basilar membrane; E, inner hair-cells; i, i', membrana reticularis; 2, 2', 2", 

 rows of outer auditory hairs projecting between phalanges (4-4") ; 5, terminal plates ; 6-6", outer 

 hair-cells ; 7-7", cells of Deiters ; 8, cells of Claudius. (After Testut.) 



rod as the phalangeal process, uniting with the adjacent pha- 

 langes of the cells of Deiters to form the membrana 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. 



