Identifier: americantextbook00howe (find matches)
Title: An American text-book of physiology
Year: 1897 (1890s)
Authors: Howell, William H. (William Henry), 1860-1945 Bowditch, H. P. (Henry Pickering), 1840-1911
Subjects: Physiology
Publisher: Philadelphia : Saunders
Contributing Library: Columbia University Libraries
Digitizing Sponsor: Open Knowledge Commons

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ntand complicated one. The placenta is, technically, the nutritive organ ofthe embryo. Nutrition of the Embryo.—We have seen that a fundamental and moststriking difference between the minute human ovum and the large e^^ of thefowl lies in the relative quantity of food contained in the two. The fowl hasretained the primitive habit of discharging the ovum from the maternal body,and discharges within its shell at the same time sufficient food for the needs ofthe developing chick. Evolution has endowed the human mother, in commonwith other mammals, with the peculiar custom of retaining the offspring withinher body until its embryonic life is completed, and of doling out its nutiimentmolecularly throughout the period of gestation. The store of nutritive deuto-plasm with which the egg leaves the ovary is, therefore, only sufBcient for theearly segmentative activities. Within the Fallopian tube absorption from thesurrounding walls doubtless goes on. Arrived in the uterus and imbedded in 58
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Fig. 315.—Diagram of the placeuta (Schafer): s, pla-cental sinuses, into which project the fetal villi, con-taining the red fetal vessels ; d. s, decidua serotina; s.p,spongy layer, and m, muscular layer, of the uterus; a,uterine artery, and v, uterine vein, opening into theplacental sinuses. 914 AN AMERICAN TEXT-BOOK OE PllYSlOLOGY. its (locidiuil wall, the .segmented ovum eontimies to take nutriment from itsimmediate environing cells. It has been suggested, but without much basisof fact, that the uterine glands, which at this time are greatly dilated, mayfurnish a nutritive secretion for the use of the embryo; but, apriori, it wouldseem more reasonable that, just as the ovum within the Graafian follicleobtains its food from its surrounding stroma, so within the highly vasculardecidua it absorbs directly from the decidual tissue. But that this sourcesoon proves insufficient for the rapid growth is indicated by the early develop-ment of the chorion with its villi and the embryonic v

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