PLACENTA

(Lat.). n. f. Plaas(pla3k)-eant'a3. From TrAaxows. a flat cake. Fr., p., arriere-faix. Ger., Mutter kuchen, Gefa , kuchen (1st def.), Nachgeburt (1st def.), Samentrciger (4th def.)- 1. The afterbirth; an organ which during fretal life, in nearly all mammals, performs the function of aerating the blood of the foetus by providing the mechanism nece ary to a direct interchange of gases between the foetal and the maternal blood; consisting of a maternal portion (see Maternal p.) and a fostal portion (see Foetal p.) closely interwoven with each other, the whole organ, thus doubly constructed, being intimately connected with the internal organism by its implantation upon the interior of the uterine wall on the one hand and connected with the foatal circulation by the umbilical cord on the other. " In all mammals, so far as is yet known," says Allen Thomson, " excepting the Honotremata and marsupials, the true placental structures consist in the establishment of a close relation between finely ramified foetal blood-ve els, derived originally from the outer or mesoblastic layer of the allantois, with minutely or widely distributed blood-ve els belonging to the uterus. Both of these are, originally at least, if not throughout the whole of gestation, accompanied and supported by cellular and other constituent elements of the foetal and maternal structures to which the blood-ve els respectively belong: while the uterine glands do not appear to take any direct or important part in this combination of foetal and maternal elements." The term p. was first used by Falloppius. In China the dried human p. is used as a tonic in phthisis. [A, 45; " Proc. of the Am. Pharm. A oc.," xxiv, p. 760 (a, 50).] 2. Of Stein, a ma into which the segments may coalesce that have been formed by the breaking up of the endoplasts of two individual infusorians as the result of the conjugative act. [A, 12.] 3. Any cake-shaped formation or organism, [a, 48.] 4. (a) The trophosperm of Richard, the spermophore of Link, the receptaculum seminum of Necker, the placentary of Mirbel; the portion of an ovary that bears the ovules, or the corresponding part in the fruit carrying the seed. In vascular cryptogams the ti ue from which the sporangeia are produced, (b) The podosperm of many authors; of Mirbel and others, the point of attachment of a single ovule in an ovary, the union of such p's being called the placentary or pistillary cord. [B, 1, 19, 77, 121, 123, 279. 291 (o, 35).] Annular p. SeeZon'aryp. Axiferous p. Fr., placenta axifere. In botany, a p. springing from the base or the summit of the ovary. [B, 132.] Axile p. Fr., p. axillaire. A p. formed by the margins of the carpellary leaves of a compound pistil folding inward so completely as to meet in the centre or axis of the ovary. [B, 1. 77, 291 (a, 35).] Basal p., Basilar p. A free central p., a p. in which the ovules are borne on a column which rises free from the bottom of the ovary. [B, 77, 291 (a, 35).] Battledore p. Fr., p. a. insertion velamenteuse en raquette (ou margin ale). That form of insertion of the umbilical cord into the margin of the p. in which it spreads out so as to resemble a battledore. Bell-shaped p. See DomeAp. Deciduate p. A p. of which the maternal portion comes away at delivery. [L, 201.] Diffused p. See P. diffusa, P. memE, he; Ea, ell; G, go; I, die; I, in; N, in; N, tank; [s. 280]