. On the theory and practice of midwifery . the chorion at a more ad-vanced period of gestation, and we shall find that a new organ has beendeveloped on that part of it which is in contact with the uterus. This organwas first called the placenta, I believe, by Fallopius: it is a spongy vas-cular mass, existing in some form in all mammalia, as an appendage ofthe chorion. It is of considerable size at the termination of utero-gesta-tion, its diameter being six or eight inches, its circumference eighteen ortwenty-four, and its thickness from one inch to one and a half. In generalit is of a rounde
. On the theory and practice of midwifery . the chorion at a more ad-vanced period of gestation, and we shall find that a new organ has beendeveloped on that part of it which is in contact with the uterus. This organwas first called the placenta, I believe, by Fallopius: it is a spongy vas-cular mass, existing in some form in all mammalia, as an appendage ofthe chorion. It is of considerable size at the termination of utero-gesta-tion, its diameter being six or eight inches, its circumference eighteen ortwenty-four, and its thickness from one inch to one and a half. In generalit is of a rounded or oval form. Internally, its surface is smooth andshining, from its being covered by the chorion and amnion, beneath whichthe radiations of the umbilical vessels may be discovered. The chorion,whicn covers its inner surface immediately, is firmly attached to it, andsends processes between its lobes and lobules, whilst the amnion lyingover the chorion is but loosely attached. The outer or uterine surface, if UTERO-GESTATION. 115 Fig. the placenta be in situ or removed carefully, is uniform and levelthough not exactly smooth, being covered by the decidua serotina ; if thisbe peeled off, the lobes and lobules into which the placenta is divided,are evident, and we find processes of the decidua serotina entering thesedivisions. The vessels of one lobe have very rarely any direct commu-nication with those of another. 174. As to the formation of the placenta, we observed that the villiof the chorion diminish gradually in number, and finally disappear fromevery part of its surface, except where it is in contact with the uterus, atwhich part they become, as it were, concentrated, and grow with greatluxuriance, in consequence of the development within them of vesselsderived from the inner layer of the chorion (the endochorion), or frombetween the two layers. These vessels go on enlarging and multiplying,interlacing and anastomosing with each other, until they with their con-necti
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