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See also:PLACENTA (See also:Lat. for a cake) , in See also:anatomy, the See also:organ by which the embryo is nourished within the womb of its See also:mother . When the See also:young one is See also:born the See also:placenta and membranes come away as the " afterbirth." Inhuman anatomy the organ is a circular disk about seven or eight inches in See also:diameter and one and a See also:quarter inches in thickness at its centre, while at its margin it is very thin and is continuous with the foetal membranes . It weighs about a See also:pound . In See also:order to explain the formation of the placenta it is necessary to encroach to some extent on the domain of See also:physiology . Before each menstrual See also:period, during the See also:child-bearing See also:age of a woman, the mucous membrane of the uterus hypertrophies, and, at the period, is See also:cast off and renewed, but if a fertilized ovum reaches the uterus the casting off is postponed until the See also:birth of the child . From the fact that the thickened mucous membrane lining the interior of the uterus is cast off sooner or later, it is spoken of as the " decidua." The fertilized ovum, on reaching the uterus, sinks into and embeds itself in the already prepared decidua, and, as it enlarges, there is one See also:part of the decidua lying between it and the uterine See also:wall (" decidua serrotina " or " basalis "), one part stretched over the See also:surface of the enlarging ovum (" decidua reflexa " or " capsularis ") and one part lining the See also:rest of the uterus (" decidua See also:vera ") (see fig I.) . Decidua basalis . under Alonzo de Ojeda, by whom he was entrusted with the See also:charge of the unfortunate See also:settlement at See also:San See also:Sebastian . He accompanied See also:Balboa (whom he afterwards helped to bring to the See also:block) in the See also:discovery of the Pacific; and under Pedrarias d'See also:Avila he received a repartimento, and became a See also:cattle-See also:farmer at See also:Panama . Here in 1522 he entered into a See also:partnership with a See also:priest named Hernando de Luque, and a soldier named Diego de See also:Almagro, for purposes of exploration and See also:conquest towards the See also:south . See also:Pizarro, Almagro and Luque afterwards renewed their compact in a more See also:solemn and explicit manner, agreeing to conquer and See also:divide equally among themselves the opulent See also:empire they hoped to reach . Explorations were then undertaken down the See also:west See also:coast of South See also:America, in which Pizarro, though See also:left. for months with but thirteen followers on a small See also:island without See also:ship or stores, persisted till he had coasted as far as about 9° S. and obtained distinct accounts of the Peruvian Empire .
The See also:governor of Panama showing little disposition to encourage the adventurers, Pizarro resolved to apply to the See also:sovereign in See also:person for help, and with this See also:object sailed from Panama for See also:Spain in the See also:spring of 1528, reaching See also:Seville in See also:early summer
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