DEVELOPMENT OF THE ORGAN OF CORTI 295 



like exoplasmic head-collar develops and extends in close contact 

 with the intercellular septa, as if the material elaborated at the 

 periphery of the cytoplasm to increase the amount of extra- 

 cellular cement were prevented from leaving the cell and 

 retained within this collar, the staining capacity of which 

 gradually increases, while the more central protoplasm, the 

 endoplasm, becomes clearer and paler- This head-collar has 

 been described in the embryonic pillar cells by N. Van der 

 Stricht as 'plaque cuticulaire;' in the adult organ by Schwalbe 

 ('87) as 'ellipsoider Einschlusskorper,' by Joseph ('00) and v. 

 Spee ('01) as 'Kopfeinschluss,' and by Held ('02) as 'Kopf- 

 korper.' 3) A change in the direction of the phalanx process 

 and the intracephalic rootlets of its fibrils. Previously (fig. 1) 

 inchned almost vertically, this fibrillar bundle gradually takes a 

 more obhque course (fig. 3, oph), becoming in time nearly hori- 

 zontal (figs. 4 and 6, oph) not only outside the head, but also 

 within it, the fibrils occupying its superficial part. This altera- 

 tion is caused doubtless by the shortening and considerable en- 

 largement of the head and constitutes a striking evidence that 

 this enlargement is the result not only of a sheer expansion, but 

 also of a process of stretching of its lower parts in a more hori- 

 zontal and radial direction, as if pushed upward by the strain 

 of the elongating pillar body. At the same tune, this pressure 

 involves a conspicuous shortening of the previous cephahc seg- 

 ment. The peculiar change in the direction of the phalanx 

 process has been observed by N. Van der Stricht and by 

 Held ('09). 



Inner pillars. In the adult organ of Corti the superficial 

 portion of the inner pillar can be divided into three parts: 



The apex, or 'Kopfplatte' of Held, the ' Innenpfeilerzellen- 

 schnabel' of v. Spee and Kolmer ('09), the 'plaque cephahque ou 

 membrane fibrillaire' of N. Van der Stricht. This is a very thin, 

 quadrilateral membrane (fig. 13'), elongated radially and 

 stretched between the apices of the sustentacular cells (originally 

 the outer pillars) and the sensory cells {oh') of the first outer 

 row and the apices of the supporting {is') and acoustic {ih) 

 elements of the inner row of hair cells. It constitutes a part of 



