THE ORGAN OF CORTI 631 



derived from the terminal processes of the cochlear nerve. These 

 nerve fibrils make their exit in small bundles from the bony spiral 

 lamina, and passing outward upon the basal membrane are dis- 

 tributed 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 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 basal membrane, but are in contact 

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

 is prolonged into a broad flattened plate-like process whose inner 

 margin interdigitates with the head plate of the inner hair cells, as 

 stated above, and whose outer margin is so prolonged as to almost, 

 though not completely, 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. 



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 4,000 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 suc- 

 cessive 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. 



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 

 basal 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 con- 

 sists of a clear, finely granular cytoplasm and contains the sphe- 

 roidal 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 cuticular floor for the tunnel. This 



