DEVELOPMENT OF THE MEMBRANA TECTORIA 455 



5. In sections through the axis of the cochlea the membrana 

 has a striated or lamellated appearance. The striae curve out- 

 ward and downward from the labium vestibulare where the 

 membrane remains thin. In sections perpendicular to the lamel- 

 lae the structures of the membrana is that of a reticulum with 

 thickenings at the angles of the meshes. It is therefore neither 

 lamellar nor reticular but a chambered structure or 'honeycomb' 

 of hollow tapering cuticular tubes or chambers normally filled 

 with a fluid resembling the endolymph. The bases of chambers- 

 during development rest between the ends of the epithelial cells. 



6. The thickenings at the angles of the meshes of the reticulum 

 extend lengthwise along the whole extent of the tubes or chambers 

 and in sections through the axis give the membrane its striated 

 appearance, the striae having been variously interpreted as hairs, 

 cilia, fibers and lamellae. 



7. As the basal epithelium increases its width its cells are car- 

 ried outward, away from the modiolus. This carries the bases of 

 the growing cuticular chambers outward also, though their tips 

 remain stationary. The result is the inward inclination of the 

 chambers as they are followed from base to tip. 



8. The chambered structure of the membrana explains the 

 'border-plexus' of Lowenberg, the accessory tectorial membrane 

 observed by Hardesty, and the 'reticular structure' of the mem- 

 brana described by various investigators. 



9. In fetuses of 18.5 cm., the membrana in the upper turns of 

 the cochlea projects outward beyond the spiral organ and is 

 firmly attached to the cells of both the spiral organ and of the 

 greater epithelial thickening. In this turn the spiral sulcus has 

 not yet fully formed and the distance from the inner angle of the 

 cochlea to the pillars is fully as great as in the preceding stage. 

 Thus the position of the membrana cannot be ascribed to an 

 inward shifting of the spiral organ, but is due to its rapid de^'elop- 

 ment from the cells of the spiral organ. 



10. The attachment of the membrana to the spiral organ was 

 proved not only by sections but by dissections of both fresh and 

 fixed cochleae. 



