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Placode
placode[′pla‚kōd] (embryology) A platelike epithelial thickening, frequently marking, in the embryo, the anlage of an organ or part. Placode 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. placode
placode [plak´ōd] a platelike structure, especially a thickening of the ectoderm marking the site of future development in the early embryo of an organ of special sense, e.g., the auditory placode (ear), lens placode (eye), and olfactory placode (nose).plac·ode (plak'ōd), Local thickening in the embryonic ectodermal layer; the cells of the placode ordinarily constitute a primordial group from which a sense organ or ganglion develops. [G. plakōdēs, fr. plax, anything flat or broad, + eidos, like] plac·ode (plak'ōd) Local thickening in the embryonic ectodermal layer; the cells of the placode ordinarily constitute a primordial group from which a sense organ or ganglion develops. [G. plakōdēs, fr. plax, anything flat or broad, + eidos, like]placode a plate-like embryonic structure from which a particular organ, such as the eye, develops. |