Io8 AYERS. [Vol. VI. 



brane. In several old cats I found Hensen's ridge as a very 

 narrow stripe. Outside of Hensen's ridge, especially in the 

 basal turn, one finds several projecting, irregular lines. Finally, 

 one finds on the outer free border of the membrane a peculiar, 

 refractive cord, which appears to represent the third zone of 

 Boettcher. It is best developed in the basal turn, and is com- 

 posed of parallel, refractive, and close-set fibres, whose direction 

 is from within and below outwards and upwards {i.e. upwards 

 towards the apex of the spire). These fibres seem to be col- 

 lected into a single cord at the lower edge of the structure. In 

 the middle turn this cord is single or only ribbed, and in the 

 apical turn it is similarly constituted or else dissolved into 

 branching fibres. On the vestibular surface of the membrane 

 there are as a rule no fibrous structures present. Occasionally 

 I saw, however, in old animals especially, in the middle turn, a 

 faint indication of Loewenberg's net. 



This face arches high above the edge of the limbus to fall 

 again towards the outside. In the basal turn, consequent on 

 the height of the lamina spiralis and the limbus, the direction 

 of the membrane is towards the scala tympani. In the middle 

 and apical turns, however, it is practically parallel with the 

 basilar membrane. The tectorial membrane is thinner in the 

 basal turn and thicker in the other two. The structure of 

 the membrane is very similar to that of the rabbit. It shows 

 in both zones an oblique striation, which runs from within and 

 below outwards and upwards, which is due to the fine fibres of 

 which it is composed. The course and other characters of 

 these fibres, as well as the reactions and consistency of the 

 entire membrane, agree with what has already been given for 

 the rabbit. 



Retzius {ib) : The membrana tectoria is present in the cochlea 

 of man, as in the rabbit and cat, as a flattened, band-shaped, 

 soft, elastic structure, which runs along the whole of the papilla, 

 is somewhat narrower in the basal turn, but broader in the mid- 

 dle and apical turns. Two zones are to be distinguished. The 

 inner very thin zone is closely applied to the surface of the epi- 

 thelium of the limbus spiralis, and is fastened by means of a 

 thin, irregular, net-like, cement-substance. The inner border of 

 this zone does not reach quite to the root of the membrana 

 Reissneri, but lies nearly midway between this and the edge of 



