. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. PLACENTA —(FUNCTIONS). Fig. 487. 721. The formation of the fatal chamber more advanced than in fig. 48f>. T/ie or«»n /s sfr'# emi/y covered by vil/i, the eiiflx of which, about this time, begin to be attached to the icalls of the chamber in which the ovum is contained. o, ovum; dr, decidua reflexa, forming the foetal chamber; dv, decidua rera; u, uterine walls. ing the formation of a subcutaneous abscess ; while in proportion as the base of the chamber becomes extended by the gradual retiring, from the centre, of the
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. PLACENTA —(FUNCTIONS). Fig. 487. 721. The formation of the fatal chamber more advanced than in fig. 48f>. T/ie or«»n /s sfr'# emi/y covered by vil/i, the eiiflx of which, about this time, begin to be attached to the icalls of the chamber in which the ovum is contained. o, ovum; dr, decidua reflexa, forming the foetal chamber; dv, decidua rera; u, uterine walls. ing the formation of a subcutaneous abscess ; while in proportion as the base of the chamber becomes extended by the gradual retiring, from the centre, of the line of reflexion of the de- cidua, like waves receding from a central point, so, at the same time, an increasing surface is producedby the expansion of the uterus itself; and the layer of decidua here formed, com- monly termed the decidua scrotina, is simply the mucous membrane reproduced to supply the place of that which had been consumed or pushed off in forming the decidua reflexa. The fourth or final stage consists in the partitioning of the permanent placenta into smaller portions or lobes by the extension of the layer of decidua (serotina) which lies op- posite to the developed villi inwards at vari- ous points towards the chorion. In this wav are constructed the dissepiments already de- Sitpp. scribed as hounding the several lobes or co- tyledons. This partitioning of the placenta commences about the fourth month. Thus, during these several stages in the formation of the placenta, two processes may be said to be concurrently carried on which tend in opposite directions—a process of positive enlargement and growth combined with one of relative retrogression or limita- tion. For while the bulk of the placenta is progressively increasing up to the completion of pregnancy, the relative amount of surface of the ovum appropriated to it is, on the other hand, diminished. The entire surface of the chorion being, in the first stages of develop- ment, employed as a placent
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