128 ARRANGEMENT AND STRUCTURE OF SUSTENTACULAR CELLS 



side of the hair-cell, the latter along the outer side. This element, close to the inner 

 pillar, should be regarded as homologous to the cell of Deiters. 



The "inner phalanx cells," or supporting cells of the first inner row, with their 

 superficial phalanx-shaped apices, are accurately described in the adult organ of 

 Corti by Held (1902), who mentions in connection with the phalanx the existence of 

 a plate or process extending from the head of the inner pillar between two neigh- 

 boring apices of inner hair-cells. This plate ("Innenschnabel der Innenpfeiler- 

 zellen") has been observed also by Waldeyer (1872), Nuel (1878), Retzius (1885), 

 and Kolmer (1909). In reality it does not exist, and what has been mistaken for it 

 is probably only the dark, more superficial veil derived from the terminal bars. 



According to N. Van der Stricht (1908), the nucleated bodies of the inner sup- 

 porting cells, located in the greater ridge in the embryo bat, are found beneath the 

 inner acoustic elements, and (p. 611) "de ce segment basal, renfermant le noyau, 

 part un proplongement superficiel effile, qui s'engage entre deux cellules acoustiques 

 internes, pour atteindre la surface du neuroepithelium." This author did not recog- 

 nize the shifting of the intermediate portion of their cytoplasm towards the inner 

 pillars. 



Referring to the development of the membrane of Corti, Held (1909, p. 219) 

 mentions, inside of the row of inner phalanx cells, a row of "Grenzzellen, deren freie 

 Zellenfliichen die Kopfe der inneren Haarzellen an ihrem axialen Umfang umgrei- 

 fen, " but he does not give any further description of these elements. In his figure 

 18 Kolmer (1909, p. 309) pictures "doppelzeilige Stellung der inneren Haarzellen, 

 Kopfe der Innenphalangen und Grenzzellen, mehrreihige Anordnung der Haare," 

 but he, likewise, gives no further explanation. 



SIGNIFICANCE OF SOME OF THE SO-CALLED CELLS OF HENSEN. 



All observers are in agreement concerning the arrangement of the cells of 

 Hensen, representing them as elongated, columnar elements, extending from the 

 membrana basilaris to the free surface of the epithelium; but further investigation 

 is necessary to prove the correctness of this statement. In the earliest stage of 

 differentiation of the organ of Corti, at which time the apices of the outer hair-cells 

 attain only half the size of those of the inner (fig. 2), there can be seen in sections tan- 

 gential to the surface and outside the third row of Deiters cells, a column of elements 

 exhibiting nuclei at two different levels; two near the membrana basilaris (ad iv ), 

 and two others nearer the free surface of the epithelium (aoh lv ) . The arrangement 

 of these two sets of nuclei or nuclear groups is very remarkable; one (ad iv ) runs 

 parallel to the nuclear column of Deiters cells (d m ), the other parallel to the nuclear 

 column of hair-cells (oh iu ) . This peculiar disposition would suggest that the deeper 

 nuclei belong to the sustentacular elements and the more superficial nuclei to the 

 acoustic elements, although there is no evidence of any differentiation into sensory 

 cells at the level of their apices. 



Similar structures are seen in later stages of development, and are all the more 

 remarkable because here (fig. 5) the cytoplasma surrounding the nuclei has under- 



