748 SPECIAL SENSES 



bases attached to the basilar membrane and their summits articulated 

 above, so as to form a regular spiral arcade enclosing a triangular space 

 that is bounded below by the basilar membrane. The number of the 

 elements of the organ of Corti is estimated at about 4500, for the outer, 

 and 6500, for the inner rods (Pritchard). The relations of these struc- 

 tures to the membranous labyrinth are seen in Fig. 193. The external 

 pillars are longer, more delicate, and more rounded than the internal 

 pillars. The form of the pillars is more exactly shown in Figs. 195 

 and 196, the latter figure, however, exhibiting other structures which 

 enter into the constitution of the organ of Corti. It will be remarked 

 that a small nucleated body is attached to the base of either pillar. At 

 the summit, where the internal and the external pillars are joined 



Fig. 195. The two pillars of the organ of Corti (Sappey). 



A, external pillar of the organ of Corti : i, body, or middle portion ; 2, posterior extremity, or base ; 

 3, cell on its internal side ; 4, anterior extremity ; 5, convex surface, by which it is joined to the inter- 

 nal pillar ; 6, prolongation of this extremity. 



B, internal pillar of the organ of Corti : i, body, or middle portion ; 2, posterior extremity ; 3, cell 

 on its external side ; 4, anterior extremity ; 5, concave surface, by which it is joined to the external 

 pillar; 6, prolongation, lying above the corresponding prolongation of the external pillar. 



C, the two pillars of the organ of Corti, united by their anterior extremity, and forming an arcade, 

 the concavity of which presents outward; i, I, body, or middle portion of the pillars; 2, 2, posterior 

 extremities ; 3, 3, cells attached to the posterior extremities ; 4, 4, anterior extremities joined together ; 

 5, terminal prolongation of this extremity. 



together, is a delicate prolongation, directed outward, which is attached 

 to the covering of the quadrilateral canal. 



The above description comprises about all that is definitely known 

 of the arrangement of the pillars or rods of Corti. They are nearly 

 homogeneous, except when treated with reagents, and are said to be of 

 about the consistence of cartilage. They are closely set together, with 

 narrow spaces between them, and it is difficult to see how they can be 

 stretched to any considerable degree of tension. The arch is longer at 

 the summit than at the base of the cochlea, the longest rods, at the 

 summit, measuring, according to Pritchard, about -^ of an inch (125 /*), 

 and the shortest, at the base, about -^ of an inch (50 /A). At the base 

 of the cochlea the two sets of rods are about equal in length. From the 

 base to the apex, both sets, outer and inner, progressively increase in 



