AUDITORY ORGAN. 



example, in the guinea-pig, ten inner pillars correspond with 

 eight outer pillars (Fig. 271). The inner pillars are more 

 numerous than the outer. The heads of the latter are variable 

 in form. There is a rounded joint-surface which fits into the 

 socket of the head of the inner pillar. From this it bends 

 outward and forms a flattened oar-shaped process, which enters 

 between the upper free end surfaces of the outer hair cells, 

 which will be described later (Figs. 271 and 272). The thin 



Fiu. 272. 



Flat process of 

 outer pillar 



Outer hair Outer pillar 



ceUt 

 Piece of the or^jin of Corti of a rabbit, seen from above. X 470. 



head-plates of the inner pillars cover the heads of the outer 

 pillars and a part of the oar-like process. That these struct- 

 ures are differentiated from the cells by a kind of cuticular 

 formation is shown by their connection with nucleated masses 

 of protoplasm. " On the inner surface of the outer pillar, in 

 the angle between the foot-plate and the membrana basilaris, 

 we find such a collection of protoplasm. The inner pillar, on 

 the contrarv, possesses two similar accumulations of proto- 

 plasm, one at the base and the other on the outer surface of 

 the body of the pillar. 



External to the outer pillars we find the outer hair cells. 

 These are like the inner hair cells, with the exception that each 

 contains in the upper half in the neighborhood of the cuticular 

 border a dark round body which is known as Hensen's spiral 

 body. 



Their hairs are somewhat shorter than those of the inner 

 hair cells. They are arranged in three or four rows, which are 



