| 释义 |
‖ placenta|pləˈsɛntə|
[L. placenta cake = Gr. πλακόεις, -όεντα, contr. -οῦς, -οῦντα, flat cake, also mallow seed, f. the root πλακ- of πλάξ, πλάκα flat plate. So in It., Sp., Pg., Fr. in sense 1.]
1. Zool. and Anat. Pl. placentæ or placentas. (Originally placenta uterīna uterine cake.) The spongy vascular organ, of flattened circular form, to which the fœtus is attached by the umbilical cord, and by means of which it is nourished in the womb, in all the higher mammals, and which is expelled in parturition; the afterbirth. Also applied to a structure having a similar function in other animals, as some viviparous fishes, ascidians, etc.; see quots. 1875, 1888.
1691Ray Creation i. (1692) 65 The Fœtus..doth receive Air..from the maternal Blood in the Placenta uterina, or the Cotyledones. Ibid. 67 The Blood still circulates through the Cotyledons or Placenta. 1727–41Chambers Cycl. s.v., In women, unless in case of twins, &c. there is but one placenta. 1832Lond. Med. & Physical Jrnl. LXVIII. 72, I have observed..many placentæ expelled in natural labour. 1855Ramsbotham Obstetr. Med. 68 The term placenta was derived from its shape. 1875C. C. Blake Zool. Pref., Sharks bring forth their young alive, and nourish them while in the womb by a temporary structure called ‘placenta’. 1888Rolleston & Jackson Anim. Life 445 In Salpa the developing embryo is nourished by a placenta formed, in part at least, by follicle cells. 1923J. M. M. Kerr et al. Combined Text-bk. Obstet. & Gynæcol. xxvii. 390 In binovular twin pregnancy there are, no matter how closely the placentæ are approximated, two distinct chorions. 1950Eastman & Williams Obstetr. (ed. 10) xxv. 614 In double-ovum twins,..whether the placentas are separate or fused together, there are always two chorions and two amnions. 1975Nature 4 Sept. 62/1 One day before birth, male rat foetuses are 5% heavier than female foetuses, yet there seems to be no difference in the weights of their placentæ. 1976Clin. Obstetr. & Gynecol. XIX. 29 Placentas weighing over 600 gm usually are associated with complications of pregnancy.
2. Bot. The part of the carpel to which the ovules are attached; also sometimes applied to a structure which bears the sporangia in certain vascular cryptogams.
1677Grew Anat. Fruits vii. §5 The Seeds stuck all round about upon the Ambit or Sides of the Case; or upon a great Bed or Placenta within it. 1727Bradley Fam. Dict. s.v. Flower of Parnassus, A Membranous fruit..having..one cell full of seeds, fastened to a placenta which is often very square. 1845Lindley Sch. Bot. i. (1858) 16 In the inside of the ovary is a space called the placenta, on which the young seeds, or ovules, originate. 1875Bennett & Dyer Sachs' Bot. 395 The sporangia arise..from some of the superficial cells of the placenta or part to which the sorus is attached. |