Mother, Nurse and Infant / A Manual Especially Adapted for the Guidance of Mothers and Monthly Nurses, Comprising Full Instruction in Regard To Pregnancy, Preparation for Child-birth, and the Care of Mother and Child, and Designed to Impart so Much Knowledge of Anatomy, Physiology, Midwifery, and the Proper Use of Medicines as Will Serve Intelligently to Direct the Wife, Mother and Nurse in All Emergencies.

by S. P. Sackett

It is probable that in its passage it is nourished by the granulations which accompany it, and by absorbing the liquid secreted by the oviduct.

As the impregnated ovum is developed, the chorion, the amnion and the embryo may be observed.

The chorion, which corresponds to the membrane lining in the shell of an egg, is found covering the ovum at the earliest period that it has been seen in the uterus. It is smooth internally, but externally it is covered with short round villi, which at a later period remain only where the placenta is developed. The chorion is enveloped in a great measure by the reflected decidua; there is at the outset considerable space between the two, mostly filled at first by the villi of the chorion, though there may be between the two an effusion of blood; these villi soon disappear, and the membranes come in contact.

In that part of the chorion that is not covered by the decidua reflexa, the villi are more and more developed, and they contribute a most important part in the formation of the placenta.

At the same time that the placenta is formed, the villi on the other portion of the chorion is obliterated, so that the principal part of the chorion is a thin, colorless, transparent membrane, united outwardly to the reflexed decidua by short, delicate filaments, and inwardly to the amnion by an albuminous layer called the tunica media.

There is also between the two membranes the vesicula alba. This bears a perfect analogy to the yolk of an egg; it is the vitellus surrounded by the blastoderm. Its use is to contain nutriment for the fœtus before the development of the placenta.

The amnion is the most internal membrane of the ovum; it is continuous with the margins of the ventral opening in the fœtus, and closely envelopes the embryo in the early period. Its internal surface exhales a liquid into its own internal cavity, and in this the embryo swims freely.

As this membrane is more and more filled, it presses back the exterior liquid and thereby condenses it until the amnion comes in contact with the chorion. And since it adheres to the abdominal parietes of the fœtus, it furnishes as it extends a membranous sheath to the allantoid and umbilical vesicle, and these vessels, and all parts thus enclosed constitute the umbilical cord.

The placenta is an appendage of the chorion; it is a soft, spongy mass, constituting the principal connection between the ovum and the uterus, being destined to the hematosis and (as we suppose) to the nourishment of the fœtus. The placenta, at the termination of utero gestation, is a flattened body about an inch in thickness at the center; its shape is circular or oval, and it is from six to eight and one-half inches in diameter; its internal surface is covered by the chorion and amnion, and exhibits plainly the umbilical arteries and veins which converge to form the umbilical cord. Its fœtal portion is formed by the hypertrophied villi of the chorion, with which its circumference is continuous, and its maternal portion is continuous with the decidua, and is in fact a thickened part of that membrane. As the villi of the chorion are developed on one part of its surface, they ramify and form filaments that engraft themselves upon the uterine mucous membrane and adhere closely. At the same time there is an inverse development of the uterine vessels, which form vast numbers of loops that descend between the villi of the chorion, and extend through to the fœtal surface of the placenta. An amorphous matter is soon thrown out which unites the two parts together.

The placenta is, therefore, composed of two parts, distinct in their physiological action, though they together present but one mass to our view. One part is the fœtal portion formed from the chorion; the other is the maternal portion formed from the uterine mucous membrane, of which it is a greatly thickened part. After delivery the fœtal placenta comes entirely away with the epithelial layer of the placental decidua, and the placental distribution of the maternal vessels; a portion of the maternal vessels remains attached to the uterus.