Membrana externa, qua foetus invol-vitur, (from Chorion 2128 receptaculum). Vide H. Steph.thes

Sometimes called camisia fatus, shirt of the foetus. A name of the external membrane of the foetus. In women, as in some animals, the chorion, at the first, is without any sensible placenta. It is also said to have its name from the chorus or crowd of blood vessels which are spread on it. It adheres to the amnios by a gelatinous substance, and is divisible into two lamellae; the internal, or true chorion, is even more thin and pellucid than the amnios; whilst the external, or false chorion, is thick and opaque. This spongy chorion adheres to the uterus at every part, and grows thicker as it ap -proaches the placenta; whilst the internal lamina adheres inseparably to the inner surface of the placenta J hence it is plain, that the substance of the placenta is betwixt these two lamellae of the chorion. This membrane hath numerous lymphatic vessels; but in the human placenta, these vessels cannot be traced by injection on the amnios and chorion. The uterus, indeed, sends veins to the outer chorion; and perhaps the arteries do the same. See Decidua.

The use of the chorion is to sustain the umbilical vessels.