SEM analysis of the developing tectorial membrane in the chick cochlea.

The development of the tectorial membrane in the embryonic chick cochlea was studied using scanning electron microscopy. Chick embryos ranged in age from embryonic day 7 (E7) to post-hatching day 15. Our studies revealed that a fine filamentous matrix arose on the apical surface of the basilar papilla at approximately E7. This matrix was secreted by the supporting cells which encircled the hair cells. By E9, the early matrix had increased in volume but remained filamentous in structure, except at the inferior edge of the basilar papilla where it was condensed into a layer of laterally-oriented columns. At E9 the TM exhibited an additional layer of matrix, called the amorphous component. It appeared to originate from the homogene cell population, and attached to the early columnar matrix at the inferior edge of the basilar papilla. The two components of the TM were separated by a longitudinal ridge, called the 'track', which marked the inferior edge of the amorphous component. As the cochlea developed, the basilar papilla increased in width, the columnar component elongated and the track appeared to recede. These morphological findings point to separate developmental origins for the two components of the tectorial membrane.