. Comparative anatomy. Anatomy, Comparative. Fig. 52.—Early stage of the Fig. 53.—Embryonic area or "shield" of the blastodermic vesicle of the Hedge- blastodermic vesicle of the Rabbit after about 172 hog. EC, ectoderm; EN, endo- hours development. PS, primitive streak; 5-5, derm; L, lacunae, spaces occupied position of section represented in Fig, 54. (After by maternal blood; T, trophoblast Assheton.) (trophoderm). (After Hubrecht.) cavity much as the reptilian blastoderm lies upon the surface of the yolk, flattens and thins out to form the "embryonic shield" (Fig. 53) in
. Comparative anatomy. Anatomy, Comparative. Fig. 52.—Early stage of the Fig. 53.—Embryonic area or "shield" of the blastodermic vesicle of the Hedge- blastodermic vesicle of the Rabbit after about 172 hog. EC, ectoderm; EN, endo- hours development. PS, primitive streak; 5-5, derm; L, lacunae, spaces occupied position of section represented in Fig, 54. (After by maternal blood; T, trophoblast Assheton.) (trophoderm). (After Hubrecht.) cavity much as the reptilian blastoderm lies upon the surface of the yolk, flattens and thins out to form the "embryonic shield" (Fig. 53) in the axis of which appears an elongated thickening similar to the primitive streak of a sauropsidan embryo. At the anterior end of this mammahan streak is usually found a small pit or even a perforation extending through the "shield" into the cavity of the blastodermic vesicle—very suggestive of an abortive blastopore. It is along this mammalian primitive streak, as in the similar sauropsidan structure, that rapid cell-prohferation pro- duces a mesoderm (Fig. 54) which progressively interpolates itself between the already separated ectoderm and endoderm and spreads eventually into all regions of the embryo. The mesoderm is at first a continuous layer—unsegmented—and devoid of cavity. In a rabbit embryo the embryonic shield is established ordinarily by the fifth day of development, the entire blastodermic vesicle then having a diameter of about Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Neal, Herbert V. (Herbert Vincent), 1869-1940; Rand, Herbert W. (Herbert Wilbur), 1872-1960. Philadelphia : P. Blakiston's Son
Size: 1480px × 1689px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookpublisherphi, booksubjectanatomycomparative
