THE INTERNAL EAK 709 



from the terminal processes. of the cochlear nerve. These nerve fibrils 

 make their exit in small bundles from the bony spiral lamina, through 

 the foramina nervosa and passing outward upon the basilar membrane 

 are distributed in a plexus beneath the epithelium, some of their naked 

 processes almost immediately penetrating the epithelial layer to end 

 between the bases of the inner hair cells. 



The inner hair cells rest against the inner pillar cells, or rods, of 

 Corti's arch. This arch is formed by two rows of highly specialized 

 cells, the inner and the outer pillars., which are widely separated where 

 their bases are attached to the basilar membrane, but are in contact 

 at their free ends; in fact, the free extremity of the inner pillar is pro- 

 longed into a broad flattened plate-like process whose inner margin in- 

 terdigitates with the head plate of the inner hair cells, as stated above, 

 and whose outer margin is so prolonged as to almost, though not com- 

 pletely, cover the rounded head of the outer pillar. The head of the 

 outer pillar, being similarly flattened, expanded, and prolonged outward 

 beyond the margin of the head plate of the inner pillar cell, comes into 

 contact with the phalanges of Deiters' cells and with the cilia of the 

 outer hair cells which lie next without; they leave a space between 

 the outer pillars and the outer hair cells which is known as Nuel's space, 

 filled by a semi-fluid intercellular substance. 



The inner pillar cells are rather more numerous than the outer 

 in the entire length of the scala media, according to Retzius, there 

 are 5,600 of the former to 3,850 of the latter so that about three of 

 the expanded head plates of the inner pillars overlap two of the rounded 

 heads of the outer pillar cells. The arch formed by the opposed pillar 

 cells, being succeeded by similar arches of successive pillars, forms a 

 continuous tunnel, triangular in transection, which extends the whole 

 length of the scala media, and is known as the canal of Corti. This 

 canal is also filled with a semi-fluid substance. 



Each pillar cell is differentiated into two portions, the pillar proper 

 and the basilar cell, the latter containing the nucleus. The pillar 

 presents a fibrillar appearance, the fibrils being disposed in the long axis 

 of its body. This portion of the cell reaches from the basilar membrane 

 to the free surface of the neuro-epithelium. 



The basal part of the cell, the basilar cell, probably represents the 

 undifferentiated portion of the primordial pillar cell. It consists of a 

 clear, finely granular cytoplasm and contains the spheroidal nucleus. It 

 lies on that side of the pillar which faces the canal of Corti, the bases 

 of the opposed cells being expanded until they meet, thus forming a 



