DEVELOPMENT OF THE ORGAN OF CORTI 303 



their phalanx processes afford striking evidence of such a Uque- 

 faction. In the above description of these apical bands which 

 unite the phalanges to the outer pillar heads, the most distinct 

 constituent, the fibrillated bundle, alone has been mentioned. 

 In the early stages of the development the band is composed of 

 fibrils collected into a fasciculus, which is surrounded by a clear 

 granular cytoplasm. Before the space of Nuel reaches the 

 membrana reticularis this phalanx process proper is very short, 

 being limited to the portion running between two neighboring 

 hair cells (figs. 4, oph; 8 and 11, oph''), and the portion lying 

 under the phalanx itself (figs. 8 and 11, opU^). In other words, 

 the enlarged head contains the longest part of the fibrillar 

 bundle (figs. 8, oph'^; fig. 11, oph''', oph'^) and covers com- 

 pletely the head plate of the inner pillar. The roof of the 

 developing space of Nuel is made up of two strata, the lateral, 

 thinnest part of the outer pillar head (fig. 11, oph'''; compare 

 with figs. 6 and 12), and the lateral part of the superficial 

 striated membrane (fig. 8, ipl''). When the first interstice of 

 Nuel has attained its entire extent in the adult organ its roof is 

 composed of the lateral part of the head plates of the inner 

 pillars (figs. 13', 17, and 18, ipl'') strengthened by equidistant, 

 parallel, fibrillated bundles, portions of the ultimate phalanx 

 processes (figs. 13''', 17, and 18, oph'''), which run in an oblique 

 direction toward the spiral rows of pillars (fig. 13''). 



Figures 13', 13'', and 13''' illustrate the structures of this 

 roof at these successive levels in the adult organ of Corti. 

 Between the apices of the inner hair cells (ih) and the outer 

 sensory elements {oh') they show respectively a superficial 

 plane — the striated head-plates of the inner pillar cells (fig. 13', 

 ipl") — an intermediate plane composed of parts of the pre- 

 ceding plates (fig. 13'', ipl'') and parts of oblique subjacent 

 fibrillar bundles, and a deeper plane (fig. 13''') showing from 

 the axial to the lateral side, the row of fibrillated lamellae, heads 

 of the inner pillars (ikd), the row of outer heads," a gap nearly 

 as large as the preceding row and bridged across by equidistant 

 fibrillar bundles {oph'''), entirely devoid of clear cytoplasm. 

 The gap is the upper floor of the space of Nuel {SN'), which is 



