Page:The Works of William Harvey (part 2 of 2).djvu/42

 SCO THE MEMBRANES.

��Of the Membranes.

With respect to the membranes or tunics of the uterus ; as their special office is to contain the "waters," and as these waters are two only, it is pretty certain that the membranes themselves do not necessarily or usually exceed that number.

Those who enumerate three tunics are, I believe, in error, owing to the ancients having described the same membrane at one time under the title of " chorion," from the concourse of veins, at another under the name of " allantois" from its form.

Unquestionably, every "conception" is inclosed in two en- velopes, just as the brain is surrounded by its two membranes; every tree and fruit, moreover, has it double bark ; and lastly, seeds and fruits are protected by a double covering, the outer- most of which is harder and stronger than the inner one.

Of the above-mentioned membranes, the innermost (that which contains the colliquament or purer fluid,) is exceed- ingly delicate ; it is called the " amnion," i. e. the mantle, from the way in which it is disposed round the fetus. The outer tunic, however, is much thicker and stronger, and has received the name of " chorion," " because," says Fabricius, " a multitude of arteries and veins are aggregated together and arranged in it, as it were, after the manner of a chorus. Hence one of the tunics of the eye has been denominated ^opoet&j/c (choroid) from its vessels having a similar arrangement to those in the chorion ; the plexus of arteries and veins in the ven- tricles of the brain has also gained its name from the same circumstance."

The chorion fills the whole uterus, and contains a viscid and rather turbid fluid ; whilst the placenta, or carunculse, adhere to its outer surface, and thus attach the " conception" to the uterus.

In the woman it is usually adherent to the amnion at its lower portion ; nor can it be separated there without diffi- culty. In cloven-footed animals the chorion is of very large size, and contains a hundred times more fluid than the amnion: this last membrane at first is scarcely as large as a nutmeg, or broad beau, and is generally found in one or other horn of the uterus ; that, namely, in which the embryo lies.

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