The Early Development of the Otic Vesicle in Staged Human Embryos Available to Purchase

The early development of the otic vesicle has been investigated in thirty-six human embryos from stage 9 to stage 18 (3 to 6 post-ovulatory weeks).

The otic zone was first distinguished at stage 9 and invagination had commenced in the more advanced specimens of stage 10. The otic pit deepened progressively during stage 11, and certain resemblances to the developing lens were noted. It is believed that contributions from the wall of the otic pit to the vestibulocochlear crest occurred, e.g. at stage 12, but they were not as conspicuous as the corresponding crest migrations from the optic primordium to the sheath of the optic vesicle. The otic pit became closed from the surface at stage 13 to form the otic vesicle, the dorsomedial portion of which became recognizable as the endolymphatic appendage.

As in the case of the lens, a part of the basement membrane of the surface ectoderm became invaginated (stages 11 to 13) to form the basement membrane surrounding the otic vesicle.

Although their precursors were detectable earlier, the cochlear and the semicircular ducts were clearly defined by the end of stage 18. During the formation of the semicircular ducts, portions of the epithelium lost their identity and their basement membrane disappeared, so that the epithelium merged with the underlying mesoderm, and obliteration of portions of the cavity of the otic vesicle ensued.

It has been established previously that the various basement membranes associated with the embryonic eye persist into adulthood. Moreover, it is known that at least certain portions of the adult membranous labyrinth possess a basement membrane, derived presumably from that surrounding the otic vesicle in the embryo. The possible existence of a continuous and intact basement membrane throughout the adult membranous labyrinth, however, seems to require further investigation.