DEVELOPMENT OF THE MEMBRANA TECTORIA 429 



urements show conclusively that the pillar cells have actually 

 approached the inner angle oi the cochlea a sufficient distance 

 to warrant the change in position of the membrana tectoria. 

 This point will be taken up in describing our own preparations. 

 Hardesty describes an accessory tectorial membrane lying beneath 

 the tectorial membrane proper and extending from near its outer 

 edge to Hensen's stripe. It is composed of two sets of fibers 

 crossing at an acute angle. In his figures these fibers form a 

 network with diamond shaped meshes. Hardesty does not state 

 how this accessory tectorial membrane is developed. Hensen's 

 stripe, a line which has been described as extending lengthwise 

 along the underside of the tectorial membrane, Hardesty regards 

 as due to the intercrossing ends of the fibers composing the 

 membrane. He states that its position corresponds to the line 

 of enclasped phalanges of the pillars. Hence the stripe of Hensen 

 should lie between the inner and outer hair cells. Hardesty 

 believes that it has an embryological significance: "Hensen's 

 stripe seems to be the expression of the period at which the 

 retrogression of the epithelium began. It also represents the 

 line along which the thick, outer edge of thickening was last 

 attached and along which growth was last contributed to the 

 membrane." 



Held ('09) has made a detailed restudy of the development of 

 the organ of Corti and the membrana tectoria in the ear of the 

 guinea-pig, rabbit, pigeon and chick. He finds that the membrana 

 tectoria is developed as cuticular fibers by the cells of the basal 

 epithelium of the cochlear duct. An outer cuticular layer is first 

 formed over the greater epithelial thickening; later growth con- 

 sists in the secretion of the fibers by the cells of both thickenings, 

 the hair cells alone taking no part in their development. Thus 

 he holds that the membrana tectoria is developed in situ over 

 the organ of Corti. Owing to the later elongation of its cells 

 the organ of Corti shifts its position inward (axially) but this 

 shifting is not extensive enough to account for the position of 

 the membrana tectoria, which overlies and may project beyond 

 the cells of the organ. In the adult fowl Held found that the 

 membrana remains attached to the supporting cells of the sensory 



