370 MICROSCOPIC ANATOMY OF THE ORGANS. 



These parts are the inner and outer segments of the organ of 

 Corti, and are situated on either side of Gorki's arch. 



In Fig. 270 it is seen that the epithelial cells from the sul- 

 cus spiralis internus outward become higher and pass over into 

 the inner segment of the organ of Corti. Two kinds of cells 

 can be recognized in this region. Those of one kind are pro- 

 vided with fine hairs on the upper free surface, and are known 

 as the inner hair cells or auditory cells. They are arranged in 

 a row bordering on the arch of Corti. They are cylindrical 

 structures, whose lower thickened parts contain large nuclei. 

 They do not rea^h to the rnembrana basilaris. 



The upper free surface of these cells is marked by a cutic- 

 ular border which is broader than the upper end of the cell 

 body ; and carries about twenty fine stiff hairs. These are 

 essentially sense cells, entering into communication with the 

 terminal ramifications of the cochlear nerve fibres. 



Just internal to the hair cells we find three or four rows of 

 high cells which act as supports for the hair cells. These are 

 called the supporting cells or inner roof cells. 



Toward the outside the hair cells lie on the cells of Corti's 

 arch. The latter consist of two rows of so-called pillars (pillar 

 cells). We distinguish the inner pillars and the outer pillars of 

 the arch (Figs. 271 and 272). These are somewhat S-shaped, 

 and lean toward one another, so that their upper ends are 

 joined, and lower ends resting on the rnembrana basilaris 

 are far apart. In this way they form an arch arcus spiralis 

 which partly encloses the canal of Corti. 



The inner pillars are strong fibres, each spread out at its 

 base to form a foot-plate resting on the membrana basilaris. 

 The upper end (head end) is thickened and hollowed to form a 

 socket, in which the head of the outer pillar fits. The length- 

 ened upper part forms a flat process or head-plate overlying 

 the head of the outer pillar. The middle part or body of the 

 pillar is thin, and shows on close examination a striation which 

 indicates a fibrous structure. 



The outer pillars are constructed similarly. They are some- 

 what larger and broader than the inner pillars, so that, for 



