A textbook of obstetrics . Fig. 62.—Diagrammatic sectionof a mammalian blastoderm after thecover-cells have completely closed inthe blastoderm, and the embryo properhas become two-layered: ep\ Non-em-bryonic epiblast; epy embryonic epi-blast; hy, hypoblast; ys, yolk-sac(from Haddon). Regarding thethe ovum, an entoderm,surface ofoval, opaque region maybe observed (the embryonalarea), and in the middle ofthis area a streak of greateropacity appears,—the prim-itive streak. At the site ofthis streak a depressionnext appears,—the prim-itive groove. A microscopicexamination of a sectionthrough this
A textbook of obstetrics . Fig. 62.—Diagrammatic sectionof a mammalian blastoderm after thecover-cells have completely closed inthe blastoderm, and the embryo properhas become two-layered: ep\ Non-em-bryonic epiblast; epy embryonic epi-blast; hy, hypoblast; ys, yolk-sac(from Haddon). Regarding thethe ovum, an entoderm,surface ofoval, opaque region maybe observed (the embryonalarea), and in the middle ofthis area a streak of greateropacity appears,—the prim-itive streak. At the site ofthis streak a depressionnext appears,—the prim-itive groove. A microscopicexamination of a sectionthrough this region nowshows the development ofa median layer of cells (themesoderm), made up ofcells derived in part from alayer furnished by the ecto-derm and by another fur- Head- Fig. 63. — Fmbryonic area of rabbit em-bryo : Primitive streak beginning in cell-proliferation, known as the node of Hensen (E. v. Beneden). 1 Tt is not intended to give more than a mere sketch of the development of theembryo. The student interested in the subject is referred to special works, such asMinots Embryology. 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- rrimitive groove. Beginningamnion fold.
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectobstetrics, bookyear1
