DEVELOPMENT OF THE ORGAN OF CORTI 301 



former situated between the outer acoustic elements of the 

 first and second rows, the latter between those of the second 

 and third rows. The second and third spaces do not extend 

 between the long subjacent cell bodies of the supporting 

 elements. 



Appearance of the first spiral space of Nuel. This doubtless 

 develops before the others and before any trace of the tunnel of 

 Corti. The first trace of its appearance may be seen rarely 

 (fig. 1) before the enlargement of the future heads of the outer 

 pillars, in the form of clear, vacuolated, prominent vesicles on 

 the lateral surfaces of the outer rods of Corti. How these 

 vesicles are produced is uncertain; they seem to be only transi- 

 tory and appear rather abruptly, as though due to pressure 

 within the clear fluid contained in the vacuolated medial zone 

 of the outer pillars, and as though part of this fluid had been 

 driven across the outer fibrillated zone of the cell to give rise to 

 large prominent vacuoles. These are seen along the lateral 

 surfaces of the intermediate, the basal, and occasionally even 

 parts of the superficial portions of the outer pillars. In more 

 advanced stages their outlines and connections with the secreting 

 cells become indistinct, and the vesicles are replaced by a com- 

 mon fluid mass, pervaded by a few delicate trabeculae in process 

 of disintegration or liquefaction (fig. 3, SN). This process is 

 not unHke that of cytolysis by which the fluid of the tunnel is 

 produced. It is noteworthy that a distinct outhne or a super- 

 ficial membrane is never seen, either on the lateral surface of the 

 outer pillars or on the medial surface of the inner pillars; so that 

 under special conditions of intracellular pressure, fluid may 

 exude and pass into intercellular channels. The cleft, filled up 

 with this fluid, is the first space of Nuel. It enlarges gradually 

 and extends toward the membrana basilaris, from which, even 

 in the adult cochlea, it is separated by the lateral expansions of 

 the feet of the outer pillars. 



From this description it would appear that the initial domi- 

 nant factor in the development of the cleft corresponds to a 

 difference in pressure in two parts of the outer pillars: the large 

 vacuolated medial zone, where clear fluid is being accumulated, 



THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 30, NO. 3 



