AND HAIR-CELLS IN THE DEVELOPING ORGAN OF CORTI. 125 



filament, extending uninterruptedly from the basilar membrane to the membrana 

 reticularis. This filament rests upon the basilar membrane with a fibrillated trian- 

 gular foot, and runs through the nucleated cell body in a direction parallel with the 

 axis of the cytoplasma, but occupying the medial part of the latter. The filament 

 is not axial, but paraxial (fig. 16, d', d", d'"), and is in direct continuity with another, 

 which occupies the axis of the cytoplasmic phalanx process (fig. 21, d', d", d"'), 

 and may be termed the apical filament. Whereas the paraxial filament originally 

 (fig. 16) courses through the inner part of the body of the supporting element, curves 

 about its apex, and continues along with the apical filament (fig. 21, d 1 , d"), it later 

 traverses the cell body obliquely, since above the nucleus (fig. 18, d', fig. 8, d', d", 

 d"'), and in still more advanced stages at the level of the nucleus (fig. 9, d', d"), it 

 blends with the axis, reaching the lateral part of the cytoplasm and extending into 

 the apical process. This singular modification in the course of the paraxial filament 

 at the level of the segment of support is undoubtedly due to the latter's peculiar 

 process of development and furnishes striking evidence that it extends unequally 

 (fig. 16, d 1 ), as above mentioned; that is, more toward the hair cell supported by it 

 in the third stage of development (oh 1 ) than towards the one supported by it in 

 the first stage (oh 11 ), hence more inwardly than outwardly. 



The apparatus of support is completed by the appearance of a third fibrillated 

 filament, the axial filament of the sustentacular segment of the cell of Deiters, 

 expanding into a fibrillated, chalice-like enlargement which develops in the wall of 

 the cup-shaped depression. The first trace of this axial filament and its apical 

 chalice is illustrated in figure 1 1 (d 1 ) . On tracing the paraxia 1 filament of the cell of 

 Deiters of the first row (d'), from the region of the nucleus towards the hair-cell 

 (oh'), it is seen to divide into two branches just at the point where it reaches the axis 

 of the cell. One branch (the outermost) runs outside the acoustic element and 

 represents the apical filament; another very short branch (the innermost, visible in 

 three cross-sections) is the axial filament which blends with and is replaced by a 

 deeply staining semicircle, partially surrounding the cytoplasmic pole of the acoustic 

 element (oh') and imperfect on the inner side of the latter. This incomplete ring is 

 the cross-section of an elongated, still imperfect goblet the chalice in process of 

 development. The cells of Deiters of the second and third rows also exhibit the 

 apical filament, the axial filament, and the chalice (fig. 11, d", d ;ii ). The appa- 

 ratus of support is thus composed of a paraxial filament or stem, which divides into 

 two branches, an apical filament and an axial filament with its chalice. Figure 23 

 shows parts of these structures (d 1 ) at a more advanced stage when the susten- 

 tacular segment of the cell of Deiters has reached nearly its full extent and contains 

 a much longer axial filament in continuity with the chalice. 



CONNECTIONS BETWEEN THE INNER HAIR-CELLS AND THEIR SUSTENTACULAR 



ELEMENTS. 



All authors agree that the greater epithelial thickening of the cochlea is made 

 up of elongated, columnar cells, which undergo many changes and become con- 

 verted, at the level of the sulcus spiralis, into a simple row of rather low, columnar 



