STANDARD ATLAS OF THE GROSS-ANATOMY OF THE DEVELOPING INNER-EAR OF THE CHICKEN

During development, the chicken inner ear undergoes a series of morpho logical changes which give rise to the various structures found in the adult, including the mature semicircular canals, utricle, saccule, co chlear duct, endolymphatic duct and sac, and neurons of the eighth cra nial nerve ganglion. Beginning as a hollow epithelial sphere, the inne r ear is sculpted into this complex labyrinth of fluid-filled ducts pu nctuated by their associated sensory end organs. In this report, the t hree-dimensional complexity of the developing inner ear of the chicken embryo is documented in the form of a standard atlas. The protocol in volved fixation, dehydration, and clearing of embryonic heads harveste d at daily intervals, followed by injection of an opaque dye (enamel p aint suspension) into the fluid ducts of the inner ear. The position o f the ear is shown relative to surface landmarks at seven different st ages of development, ranging from embryonic day 5 (E5) to E18. Also sh own are higher-power photomicrographs of the inner ear in isolation ta ken at daily intervals at E3-E17 and viewed from two orthogonal positi ons. Three orthogonal views are shown at B-hour intervals during the c ritical stages of semicircular canal formation (E6-E7). Quantitative m easurements of the linear dimensions of the inner ear (dorsoventral, a nteroposterior, and mediolateral axes) as a function of time indicate a linear increase in the growth of the ear from E3 through E18. This a tlas should prove valuable for evaluating mutant phenotypes in inner e ar morphogenesis following gene perturbation experiments in the chicke n. (C) 1996 Wiley-Liss, Inc.