No. I.] THE VERTEBRATE EAR. 109 



the labium vestibulare. At this place one finds on the lower 

 surface of the membrane a fine spiral stripe. The second zone 

 of the stripe is suspended free over the sulcus spiralis internus 

 and the papilla, rises towards the vestibular scala in the middle 

 and apical turns, and thickens in the middle of its body, but 

 remains thin in its free border, which here reaches scarcely to 

 the outer row of hair cells. At the free border of the outer 

 zone in the basal turn is found a thick, refractive marginal cord, 

 which bends inward as it passes upwards. In the middle turn 

 it forms a coarse-fibred, and in the apical turn a thin-fibred net, 

 whose fibres project outwards free over the outermost hair cells. 

 Occasionally one finds in the adult, especially in the apical turn, 

 on the upper plates of the outermost Deiters's cells, the fibre 

 piece, which is evidently a rudiment of the fibres which in 

 embryonic life serve to attach the membrana tectoria. 



Retzius did not find Loewenberg's net, or its equivalent, in 

 man. About the middle of the lower (tympanal) surface of the 

 membrane one finds Hensen's stripe. In the basal turn it lies 

 somewhat nearer the inner border of the zone, in the middle 

 and apical turns nearer the middle of this zone. In man this 

 structure appears in the form of a somewhat refractive, rela- 

 tively broad and flat plate with parallel contours, which lie over 

 the inner hair cells, or more correctly immediately within this 

 row. Both zones of the membrane are composed, as in the 

 rabbit and cat, of innumerable extremely fine fibres, which 

 withstand the action of acetic acid very well. Their course is 

 from the base and within, outwards and upwards. 



Retzius (1884, 237) says of Boettcher's observations in criti- 

 cism of that observer's views : — 



"Die membrana tectoria erstreckt sich mit dicker gewordner 

 ausserer Zone bis iiber die gegend der ausseren Haarzellen ; 

 in der Spitzenwindung aber kaum bis zur zweiten Reihe, wah- 

 rend ihre Fasern {mcf.) zwischen den mit frei ausragenden 

 Haaren versehenen Haarzellenoberflachen zu den Phalangen 

 der Deiterschen Zellen gehen. In der Mittel- und der Basal- 

 windung sind diese Fasern abgebrochen und nur Reste von 

 ihnen bewahrt ; an der dritten Phalangenreihe sieht man helle 

 Fasern {incf.) aufragen, und nach oben-innen vom Membran- 

 rande nimmt man andere Partien der gleichsam zuriickge- 

 schnellten absebrochenen Fasern wahr. Es ist diese Thatsache 



