The Mature of the Tectorial Membrane 145 



parallel edges. Traced to the main body, it was found to be lifted off 

 for some distance and to lie upon the main body much as a ribbon 

 would appear if lifted by the end from slight adherence to a surface. 

 Fig. 3 is an attempt to imitate this appearance of the structure, as 

 seen in the preparation, the end of the main body, however, not 

 being shown as broken, but being utilized to show the arrangement and 

 relations of the fibers of the body. When viewed in its undisturbed 

 position, it appears lying upon the under surface, as shown in Figs. 

 1 to 5, Ac, and so delicate it is, that one unaware of its presence, 

 especially upon unstained or darkly stained pieces of the membrane, 

 might consider the appearance produced by it as due to mere disturb- 

 ances in the arrangement of the fibers of the under surface of the main 

 body. That it lies practically free or, at least, very lightly adherent 

 to the under surface of the main body is indicated by the apparent ease 

 with which it comes away and by its occasional total absence from 

 broken pieces. During its further study upon various preparations, 

 short extents of it were at times seen crumpled away and free from 

 the under surface, and at times deviating inward or outward from its 

 general alignment. In several cases the deviation outward was suffi- 

 cient for a small portion of its outer edge to project beyond the outer 

 edge of the main body. Because it seemed to have a practically separate 

 existence, it is referred to here as an Accessory Tectorial Membrane. Its 

 structure, its delicacy, and its position explain the difficulty with which 

 it is distinguishable and suggest that the probable reason it has not been 

 noted before is because none of the investigators using teased prepara- 

 tions happened to obtain pieces of it isolated, extending free and undis- 

 torted, in the field of the microscope. 



In shape and structure this accessory membrane somewhat resembles 

 a long comb, the tapering teeth of which, however, are in the form of a 

 net consisting of two sets of parallel fibers all continuous into the %ack 

 of the comb" which is the outer edge of the membrane. The direction 

 of one set of the fibers coincides with the direction of the fibers in that 

 zone of the under surface of the tectorial membrane over which they 

 lie. Thus, this set of the fibers cannot be distinguished when the 

 accessory membrane is in position (Fig. 3). The other set of fibers 

 crosses the first set obliqi^ely, arising at acute angles to outer edge of 

 the membrane and coursing in a decided slant pointing toward the 

 apex of the cochlea. The fibers are embedded in a thin film of trans- 

 parent matrix of the same character as that supporting those of the 



