386 O. VAN DER STRICHT 



Hensen ('63, 71), Gottstein (70, 72), Nuel (78), Tafani ('84), 

 Retzius ('84), and by most of the more recent authors; but the 

 appearance and extension of these structures and the mechanical 

 factors taking part in their fonnation require more careful 

 study. N. Van der Stricht has shown that the head-plate of 

 the inner pillar is originally represented by a very small square 

 field, the apex of the cell, which becomes fibrillated and extends 

 over the enlarging head of the outer pillar, the foniier under- 

 going great pressure from the latter The outer pillar cells 

 originally belong to the first spiral row of outer sensory elements. 

 As development advances they are pressed out from this row 

 towards the inner rods of Corti and form a new row of outer rods, 

 the apices of which always remain fixed between those of the 

 outer acoustic elements of the first row. Hence there persists 

 an apical segment of the outer pillar, which runs obliquely from 

 the apex or phalanx of the cell, downward and inward toward 

 the future head of the pillar. This oblique process contains a 

 bundle of fibrils which, issuing from the head, passes between 

 two outer acoustic elements and spreads out upon the phalanx — 

 the head-plate of the outer piljar. By enlargement of the headj 

 the fibrillar bundle 'gradually acquires a more horizontal position. 

 Held ('09, p. 109) seemingly ascribes the head-plafce of the inner 

 pillar not only to the apex, but also to the superficial portion of 

 the cell, ''der obere Zellteil welche die Faserrohre enthalt," and 

 which is pressed flat from the developing head of the outer 

 pillar. Although he did not recognize the original position of 

 the outer pillar cells within the first row of outer acoustic ele- 

 ments, he nevertheless observes the squeezing of their 'Kopf- 

 platte,' which becomes thinner from compression between two 

 hair cells, and also of the bundle of fibrils, which at first run 

 obliquely, then at right angles to the intermediate piece of the 

 outer pillar, due to pressure from the elongating pillar cell. 



In the present paper the appearance of the tunnel space, the 

 development of the heads and cephalic appendages of the pillar 

 cells, and the formation of the Nuel spaces will be dealt with in 

 order. 



