. A treatise on obstetrics for students and practitioners . , and hence no clear idea has been gained of its methods of for-mation. It apparently rises at the sides of the embryo from the allan-tois and the edge of the yolk-sac. The chorion, the membrane whichalways remains next to the uterus or furthest from the embryo, isformed by an outer layer of the ectoderm with an inner layer of meso-derm. It completely surrounds the ovum in the early stages of itsdevelopment. An interesting idea of the early appearance of the em-bryo is obtained from the earliest specimen which has been carefullystudie
. A treatise on obstetrics for students and practitioners . , and hence no clear idea has been gained of its methods of for-mation. It apparently rises at the sides of the embryo from the allan-tois and the edge of the yolk-sac. The chorion, the membrane whichalways remains next to the uterus or furthest from the embryo, isformed by an outer layer of the ectoderm with an inner layer of meso-derm. It completely surrounds the ovum in the early stages of itsdevelopment. An interesting idea of the early appearance of the em-bryo is obtained from the earliest specimen which has been carefullystudied, that of Reichert. There is good reason for believing that thiswas not more than thirteen days old. It was a flattened sphere 3^-by 5j5q- millimetres. At its two poles or extremities it was smooth, buthaving a fringe of tuft-like processes (villi) separating the smooth areasaround the poles. On opening the embryo a mass of cells was foundnext to that portion which had been nearest the uterus, and also a meshor network of threads without nuclei. Fig. Embryo of four weeks, showing vitelline membrane and chorion. Showing the developmentof the limbs, heart, and liver. (Schultze.) The villi gradually spread and become branched, and at about thetwelfth or fourteenth day the ovum is enclosed in the decidua, the tipsof the villi alone touching the uterine decidua, and thus enabling nour-ishment to pass through the cells of the decidua into the villi of theovum. The human ovum is remarkable for the very early appearanceand development of its chorion with the chorional villi. As the am-nion develops the space between it and the embryo becomes filled withfluid, known as the amniotic liquid. At the time when the chorion is first fully developed, the contents THE GROWTH AND DEVELOPMENT OF THE EMBRYO. 73 of the chorionic vesicle—that is, the embryo surrounded by the cho-rion—are, first, the embryo, the stalk of the allantois, and the yolk-sac,and also the choriouic fluid. Concerni
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectobstetrics, bookyear1
