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The less pure are cast to the outside, and with these seed is circled round and the membrane made, in which that seed that is most pure is wrapped round and kept close together, that it may be defended from cold and other accidents, and operate the better. The first thing that is formed is the amnios; the next the chorion; and they enwrap the seed round like a curtain.
The principal attention required for young pigs is protection against being crushed by the mother. The cutting off and ligation of the umbilical cord at a point a few inches from the abdomen, and applying tincture of iodine or any reliable disinfectant is very advisable in the colt and calf. The external envelope, the chorion, is exactly adapted to the uterus.
But they afterwards disappear from one part of the surface, and grow proportionately thicker on the other part. The former has only a few small villi or none at all; the latter is thickly covered with large and well-developed villi; this alone now constitutes the placenta. This discoplacenta lies on one side of the chorion.
These four vessels before mentioned, viz., one vein, two arteries and the urachos, join near the navel, and are united by a skin which they have from the chorion and so become like a gut or rope, and are altogether void of sensibility, and this is that which women call the navel-string.
It weighed eight pounds and consisted of a male fetus of full term with six teeth; it had no odor and its sac contained no liquid. The bones seemed better developed than ordinarily; the skin was thick, callous, and yellowish The chorion, amnion, and placenta were ossified and the cord dried up.
Setting aside the name given to this by the Greeks and Latins, it is called in English by the name of secundine, after-birth or after-burden; which are held to be four in number. The first is called placenta, because it resembles the form of a cake, and is knit both to the navel and chorion, and makes up the greatest part of the secundine or after-birth.
The chorion is an outward skin which compasseth the child in the womb. The amnios is the inner skin which compasseth the child in the womb. The alantois is the skin that holds the urine of the child during the time that it abides in the womb. The urachos is the vessel that conveys the urine from the child in the womb to the alantois. I now proceed to
Twins and triplets, being quite common, will not be considered here, although there are 2 cases of interest of the latter that deserve citation. Sperling reports 2 instances of triplets; in the first there was 1 placenta and chorion, 2 amnions, and the sex was the same; in the second case, in which the sexes were different, there were 3 placentas, 3 chorions, and 3 amnions.
There is no real coalescence of the two placentas at any part of the surface of contact. Hence at birth the foetal placenta alone comes away; the uterine placenta is not torn away with it. The formation of the placenta is very different in the second and higher section of the Placentals, the Deciduata. Here again the whole surface of the chorion is thickly covered with the villi in the beginning.
This latter portion, the veil that passes from the edge of the placenta, is formed of the two membranes we have mentioned, namely, the chorion and the amnion. The placenta is, for the most part, a highly developed portion of the chorionic membrane, which became specialized simply because it happened to receive the best supply of blood.
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