428 C. W. PRENTISS 



of the labium vestibulare, of the spiral sulcus and the inner 

 portion of the spiral organ. The lesser or outer ridge gives rise 

 to the outer portion of the membrana tectoria, and later forms 

 the outer portion of the spiral organ. In the new-born guinea- 

 pig the tectorial membrane loses its connection with the organ 

 of Corti, probably owing to a dissolution of a portion of the 

 membrane. The membrane makes its appearance before the 

 differentiation of the organ of Corti or of the hair cells. In 

 structure it is a cuticular reticulum which later becomes swollen, 

 convex above and is detached from the spiral organ by the 

 secretion of endolymph beneath it. No cilia or hairs were ob- 

 served by Rickenbacher until after the differentiation of the organ 

 of Corti, and then only the hairs of the auditory cells appeared. 

 He does not state definitely just how the cuticular reticulum of 

 the membrane arises nor does he account for the striated or 

 lamellar structure which is characteristic in ordinary preparations 

 and which he figures. 



Hardesty ('08) in restudying the development of the membrana 

 tectoria finds it first in embryos of 3 cm. as a ''cuticular film of 

 appreciable thickness and decided fibrous character." Of the two 

 epithelial thickenings in the basal epithelium the inner only takes 

 part in forming the membrana tectoria, the outer giving rise only to 

 the spiral organ (of Corti). ''Not till pigs of about 14 cm., do 

 any preparations show evidences of differentiation of the cells of 

 the lesser thickening into what will become the organ of Corti," 

 says Hardesty. He thus agrees with Rickenbacher that the mem- 

 brana is quite well formed before the hairs of the auditory cells 

 appear, thus proving false the conclusions of Ayers. As he con- 

 tends that the membrana does not develop over the spiral organ 

 (though his figure 10 does not bear out this contention) Hardest}^ 

 must account for its later position over and extending to the 

 outer side of the hair cells. This he does by maintaining that 

 owing to the retrogression of the cells which originally fill the 

 spiral sulcus, there is an inward displacement of the spiral organ 

 which thus causes the outer portion of the membrana to rest 

 above and beyond it. Just how this can take place without a 

 shortening of the basal membrane is not stated, nor do his meas- 



