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A platelike epithelial thickening, frequently marking, in the embryo, the anlage of an organ or part.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



the rudiment of a sense organ or ganglion in humans, vertebrates, and some invertebrates. Placodes are paired thickenings of the outermost embryonic germ layer, the ectoderm; they arise as the nervous system is laid down in the early stages of embryogeny. In vertebrates, placodes give rise to the olfactory organ, the crystalline lens of the eye, the inner ear, the auditory ganglion, and the ganglia of the facial, glossopharyngeal, and vagus nerves. In cyclostomes, fishes, and many amphibians, placodes give rise to the lateral-line organs in addition to the aforementioned structures.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
We believe that the proboscis in this report was from the accessory nasal placode.
The presence of cellular debris resulting from cell death in the deepest aspects of the invaginating nasal placodes, as well as overall growth retardation of the facial prominences, leads to inability of the facial prominences to contact and fuse (rev by Sulik, 1988).
The nasal placodes (olfactory placodes) arise from the medial aspect of the lower portion of the frontal prominence, and the lens placodes arise from the lateral aspect of the lower portion of the frontal prominence.
The literature of embryology describes that the mesenchyme covering the caudal surface of the forebrain proliferates with surface ectoderm to form frontonasal process and the two ectodermal thickenings (nasal placodes) arise on each side of the depedent part of the frontonasal process (Johnson, 1989).