14:4 Irving Hardesty 



membrane in such a position that the line of the phalanges of the rods of 

 Corti about coincide with Hensen's stripe. 



The greater width and thickness acquired by the tectorial membrane 

 as its apical end is approached may be explained as due to the longer 

 persistence and greater width attained by the apical portion of the 

 greater epithelial thickening, noticeable in sections of foetal cochleae. 

 All signs of the thickening may have disappeared in the basal coil when 

 the coil of the apex may show considerable of the epithelium, and, in 

 the adult, the floor of the spiral sulcus, as well as the entire spiral 

 lamina, is left considerably wider in the apical than in the basal coils. 



An Accessory Tectorial Membrane. 



Though this structure as I shall describe it is undoubtedly present in 

 my preparations, its description is entered into with some hesitancy 

 because of the fact that in none of the papers I have been able to 

 examine is such a structure noted for either the pig or other animals. 

 The only explanation of why it has not been described before now is 

 offered in the fact that it is so thin and fragile and so susceptible to 

 the action of reagents that, with its existence not realized, it is impos- 

 sible to distinguish in the ordinary preparations an}i;hing suggesting 

 such a structure. Even after noting it in the unshrunken teased prepa- 

 rations, in only two of my transverse sections of the tectorial mem- 

 brane, the best I have been able to get, could there be distinguished 

 anything which might be interpreted as sections of this structure, 

 however distorted. It was not evident on some of the broken teased 

 preparations, because of the fact, soon learned, that it is apparently 

 but very slightly attached to the main body of the tectorial membrane 

 and is easily displaced or lost in the removal from the cochlea. In 

 the teased preparations after reagents found to produce shrinkage, the 

 "accessory membrane" was usually unrecognizable, appearing, from the" 

 under surface, as an irregular belt of very delicate zig-zag lines which 

 might be interpreted equally well as crumplings and shrinkage disar- 

 rangements of the surface and fibers of the main body. 



The structure was first noted in a piece of tectorial membrane 

 removed after Zenker's fluid and broken on the slide while mounting 

 it in glycerine. Under low light, it appeared as an exceedingly thin 

 transparent ribbon extending far beyond the broken end of the main 

 bodv, in places slightly twisted, but for the most part flat and showing 



