blastoderm

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blastoderm

 [blas´to-derm]
a disk of cells lying betwen the yolk sac and the amniotic cavity, from which the embryo develops.

blas·to·derm

, blastoderma (blas'tō-derm, -tō-der'ma),
The thin, disc-shaped cell mass of a young embryo and its extraembryonic extensions over the surface of the yolk; when fully formed, all three primary germ layers (ectoderm, endoderm, and mesoderm) are present.
[blasto- + G. derma, skin]

blastoderm

(blăs′tə-dûrm′)
n.
1. The layer of cells that develops on the surface of the yolk in an avian or reptilian egg and gives rise to the germinal disk from which the embryo develops.
2. The layer of cells formed by the cleavage of a fertilized mammalian egg. It later divides into the three germ layers from which the embryo develops.

blas′to·der·mat′ic (-dər-măt′ĭk), blas′to·der′mic adj.

blastoderm

A superficial layer of a fertilised egg which, in birds, is a flat disc of cells at one pole, and in insects, an outer layer of cells surrounding the yolk mass. In eggs with a large amount of yolk, cell division (cleavage) may restricted to blastoderm (meroblastic cleavage).

blas·to·derm

, blastoderma (blas'tō-dĕrm, -dĕr'mă)
The thin, disc-shaped cell mass of young embryos (e.g., reptiles, birds), and its extraembryonic extensions over the surface of the yolk; when fully formed, all three primary germ layers (ectoderm, endoderm, and mesoderm) are present.
Synonym(s): germ membrane, germinal membrane.
[blasto- + G. derma, skin]

blastoderm

the layer of cells formed by cleavage of the fertilized egg in the presence of large amounts of yolk, e.g. in birds, so that the blastoderm forms on one side of the yolk mass, initially as a small blastodisc.