A treatise on the science and practice of midwifery . evelopment of theyelk-sac; the mesoblast giving rise to the skeleton, the muscles, theconnective tissues, the vascular system, the genito-urinary organs, andtaking part in the formation of all the membranes. The Area Germinativa.—Almost immediately after the separation ofthe blastodermic membrane into lay-ers one part of it becomes thickenedby the aggregation of cells, and iscalled the area germinativa. Thisis at first round and then oval inshape, and in its centre the firstindication of the embryo may bedetected in the form of a narrowstra
A treatise on the science and practice of midwifery . evelopment of theyelk-sac; the mesoblast giving rise to the skeleton, the muscles, theconnective tissues, the vascular system, the genito-urinary organs, andtaking part in the formation of all the membranes. The Area Germinativa.—Almost immediately after the separation ofthe blastodermic membrane into lay-ers one part of it becomes thickenedby the aggregation of cells, and iscalled the area germinativa. Thisis at first round and then oval inshape, and in its centre the firstindication of the embryo may bedetected in the form of a narrowstraight line, the primitive it are some cells moretranslucent than those of the restof the area germinativa, and hencecalled the area pellucida (Fig. 54).In front of the primitive trace two elevated ridges soon arise, the lam- Diagram of Area Germinativa, showing the , j & . , . , , , Primitive Trace and Ana ivilucida. ?hid dorsaleSj winch include between them a groove—the medullary groove—and gradually unite posteriorly. 106 PREGNANCY. Fig. 55. fcSt^C^o to form a cavity within which the cerebro-spinal axis is subsequentlydeveloped. The medullary groove as it grows backward overlaps theprimitive trace, which disappears. The embryo is differentiated fromthe rest of the blastoderm by a fold anteriorly, which is called thecephalic or head fold. Another fold afterward appears posteriorly,which is called the caudal or tail fold. Laterally folds also folds all tend to grow toward the centre of the under surface ofwhat will be the embryo. The mesoblastic layer of the blastoderm, except that part which formsthe axis of the embryo, splits into an upper layer, the somato-pleure,which is beneath the epiblast, and a lower layer, the splanehno-pleure,which lies upon the hypoblast. The space formed by this cleavage ofthe mesoblast is called the pleuro-peritoneal cavity. The somato-pleureis engaged in the formation of the body walls of the embryo. Thesplanehno
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectobstetrics, bookyear1
