placodes (plak´ōds), the thick, flat sections of embryonic ectoderm on the facial surface of the embryo from which the sense organs develop.
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Alternatively, as suggested by other investigators, an embryologic explanation is also possible--"the fusion lines between neural crest-derived mesenchyme and ectoderm-derived nasal placodes may have different properties in the vicinity of the nasal dorsum and nasal tip that predispose them to the development of superficial and deep hemangiomas, respectively," they reported (Ped Dermatol.
The epidermal placodes direct dermal cells to condense (dermal
4) Waner et al noted that IH tend to develop along embryonic fusion lines of the facial placodes.
The neural crest cells are attracted to the placodes and give chase, said Mayor, whose group is learning some of the molecular details of this attraction and repulsion.
The palp, an adhesive organ differentiated in the anterior tip of the larva, is considered to have the same origin as the vertebrate anterior placodes.
It has been suggested that the ascidians possess neural crest and placodes (Jeffery et al.
The lens placodes form the lenses of the eyes in week 5, and the primary lens fibers reach the anterior wall of the lens vesicle by the end of week 7.
Stage Y&K Description 1 14 Late gastrula 2 16 Head fold 3 17 Optic vesicle 4 20 Optic cups 5 21 Auditory placodes 6 22 Lens 7 23-25 Otoliths, heartbeat, black pigment in retina and iris is strongest in periphery.
From shared lineage to distinct functions: the development of the inner ear and epibranchial placodes.
Vertebrate structures such as the neural crest and the placodes further the development of the head and the brain, which reaches an unprecedented complexity in humans.
A neurogenin-2 null mutation blocks the delamination of neuronal precursors from the placodes (Ma et al.
Londt (1983)--Revised Daspletis, presenting a key to six species: hermanni (transferred from Microstylum), hirtus, setithoracicus (established within the genus as a consequence of the synonymy of Neodysmachus), vulpes, and two new species, placodes and stenoura, both from South Africa.