A textbook of obstetrics . alled the blastula,or blastodermic vesicle. The cellsof the ovum next arrange them-selves into a thinned-out, lami-nated layer around the peripheryof the ovum, and another layerjust within this, the offspring of the central mass of cells (the ectoderm), and the proliferating central mass itself,—the entoderm. Regarding the surface of the ovum, an oval, opaque region may be observed (the embryonal area), and in the middle of this area a streak of greater opacity appears,—the prim-itive streak. At the site of this streak a depression next appears,—the prim-itive groove
A textbook of obstetrics . alled the blastula,or blastodermic vesicle. The cellsof the ovum next arrange them-selves into a thinned-out, lami-nated layer around the peripheryof the ovum, and another layerjust within this, the offspring of the central mass of cells (the ectoderm), and the proliferating central mass itself,—the entoderm. Regarding the surface of the ovum, an oval, opaque region may be observed (the embryonal area), and in the middle of this area a streak of greater opacity appears,—the prim-itive streak. At the site of this streak a depression next appears,—the prim-itive groove. A microscopic examination of a section through this region now shows the development of a median layer of cells (the mesoderm), made up of cells derived in part from a layer furnished by the ecto-derm and by another fur- 1 It is not intended to give more than a mere sketch of tin- development of theembryo. The studenl interested in the subject is referred to special works, such asMinots Embryology ? Fig. 63. Embryonic area of rabbit em-bryo: Primitive streak beginning in cell-proliferation, Known as the node of I len-en 1 E. \ ? Beneden). CHANGES IN OVUM FOLLOWING IMPREGNATION 73 nished by the entoderm. In the course of its development themesoderm develops lateral reduplications and parts into two layers(the parietal and visceral layers) inclosing spaces,—the body-cavity, or celom (Fig. 64). The parietal or somatic layer uniteswith the ectoderm to form the somatopleure. The visceral orsplanchnic layer joins the entoderm to form the splanch- Pritnitive groove. Beginningamnion fold.
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Keywords: ., bookcentury1800, bookdecade1890, bookidtex, booksubjectobstetrics
