The earliest sign of the ear in the embryo appears about the third week, and is the anlage of the complex labyrinth. It begins as an ectodermic thickening just above the first gill-cleft (hyo-mandibular). Later there is a depression of this thickened area—the auditory pit —which grows deeper and deeper, its edges finally uniting and thus forming the otic vesicle. The otic vesicle being surrounded only by mesodermic tissue is in close proximity to the after-brain and in close relation to the acoustico-facial ganglion. By repeated evaginations, invaginations, unequal growths and foldings, the complex membranous labyrinth is developed, the otic vesicle proper representing the epithelial lining of the entire labyrinth; those of its cells found in the region of the distribution of the nerve of special sense —the maculæ acusticæ and cristæ acusticæ and the organ of Corti—become highly specialized, the rest of the cells remaining as simple columnar epithelium.
STOUT GC. SOME ANOMALIES OF THE EAR DUE TO ERRORS IN DEVELOPMENT. JAMA. 1901;XXXVI(16):1097–1099. doi:10.1001/jama.1901.52470160015002d
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