Placebo.-.":-

'-bo. Anything prescribed for the purpose of pleasing or humoring the whim of a patient rather than for its therapeutic effect. (pla-sen' '-tah). an embryo or In fetus to the: wall of the uterus, and by means of which it is nourished; the ovule-bearing portion of the ovary of a plant. The mammalian placenta is a spongy ma of ti ue derived from the chorion and decidua, its evolution having begun with the differentiation of the ectoderm of the germinative area by the formation of a thickened region called the area placental is. It is a flat, circular, spongy body, adherent during gestation to the inner wall of the uterus and connected by the umbilical cord to the fetus, and forming for it the organ of nutri- Himan Placental Villi. Blood-ve els black. (From Stirling.) ion and respiration. The placenta is developed about he third month of embryonal life. The chorionic ill i in contact with the decidua reflex a cease to grow, vhile at the decidua serotina the villi become exceedigly numerous. The uterine mucous membrane in ihich the villi are embedded contributes a share to he formation of the placenta. This is known as the laternal, in contradistinction to the chorionic or fetal ortion. At term the placenta weighs one pound, is ne inch thick at its center, and seven inches in diamter. The fetal side is covered by the amnion and enetrated by the umbilical cord. The maternal irface is dark-red, irregular, and covered by the pper layers of cells of the decidua serotina. The lacenta is normally situated at the fundus, anteriorly r posteriorly. In the lower animals the placenta is different. Of the Choriata, those po e g a villous chorion, one cla , including the horse, e pig, the camel, etc., presents the villi uniformly stributed; there is no special accumulation anywhere. the other cla the villi are aggregated and specialized a particular region to form the placenta. Three.neties of placentae are generally described: (a) iat with numerous cotyledons (cow, deer, etc.); I zonal placenta (carnivora); (c) discoid placenta innkey, man. The zonal and the discoid placentae deciduate. P., Adherent, abnormal adherence the placenta to the uterine wall after childbirth.