- Local thickening in the embryonic ectoderm layer; the cells of the p. ordinarily constitute a primordial group from which a sense organ or ganglion develops. [G. plakodes, fr. plax, anything flat or broad, + eidos, like]- epibranchial placodes ectodermal thickenings associated with the more dorsal parts of the embryonic branchial arches; their cells contribute to formation of the cranial ganglia, including those of nerves V, VII, IX, and X.- lens placodes paired ectodermal placodes that become invaginated to form the embryonic lens vesicles. SYN: optic placodes.- olfactory placodes paired ectodermal placodes that come to lie in the bottom of the olfactory pits as the pits are deepened by the growth of the surrounding medial and lateral nasal processes. SYN: nasal placodes.- optic placodes SYN: lens placodes.- otic placodes paired ectodermal placodes that sink below the general level of the superficial ectoderm to form the auditory vesicles. SYN: auditory placodes.
* * *plac·ode 'pla-.kōd n a platelike thickening of embryonic ectoderm from which a definitive structure develops <ear \placode> see LENS PLACODE, OLFACTORY PLACODE
* * *n.any of the thickened areas of ectoderm in the embryo that will develop into nerve ganglia or the special sensory structures of the eye, ear, or nose.
* * *plac·ode (plakґōd) [Gr. plax plate + eidos form] a platelike structure, especially a thickened plate of ectoderm in the early embryo, from which a sense organ develops.
Medical dictionary. 2011.