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The Growth of the Offspring

womb, ovum, wall, placenta, blood and embryo

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The Embryo and the ovum which has been fertilized by the action of the male element reaches the womb it is not much larger than its original size, about the of an inch. It becomes attached to the walls of the womb in a peculiar way. Before its arrival changes take place in the inner lining mem brane of the womb, causing that lining to be come much increased in thickness, and owing to the increased thickness the surface is thrown into ridges and furrows. The small ovum ap parently is detained in the womb by falling into one of these depressions, and becoming buried; as it were, by the ridges of the thickened wall growing round and over it. About the third or fourth week after conception the ovum has become completely imbedded in the wall, in which it forms a little swelling. Meanwhile by this time the surface of the ovum is not smooth and regular as it originally was, but is covered by a set of shaggy projections, termed villi. These villi are the result of changes going on rapidly within the ovum. They become imbedded in the substance of the wall of the womb, which completely surrounds the ovum, and thus an intimate connection is effected be tween the body of the mother and the growing offspring. At this period the condition of things is represented in Fig. 210, where the ovum with the shaggy projections of its own lining membrane is shown resting on the wall of the womb, which has grown up around it so as completely to surround and cover it. The ovum is thus shut up in a little chamber in the wall of the womb, and is shut off from the cavity of that organ.

In the early period of its formation the new being is called an embryo, and in the later period before birth it is called a foetus.

It is evident from Fig. 210 that as the em bryo grows the swelling in the wall of the womb will grow larger and larger, and will gradually encroach on the space belonging to the cavity of the womb, until at length, with increased growth, the part of the wall which covers over the embryo will bulge right across to the opposite side, will, in fact, come into con tact all round with the rest of the wall of the womb, and will become merged into it. Thin

happens after the second month of pregnancy. The shaggy projections, that have been men tioned as growing out from the wall of the ovum, undergo increased growth at that part of the ovum in immediate contact with the part of the womb on which it rests, and at that place blood-vessels come to occupy their in terior. At other parts of the ovum they shrink and disappear.

Formation of Placenta or That part of the wall of the womb on which the ovum rests undergoes special development, and as the result of the special growth on the part of both the womb and ovum at that place, a special structure is formed, called the placenta, by which the structures of the em bryo and those of the mother come into inti mate relationship, and in which the blood belonging to each comes into such close con tact that exchanges of material can take place 4.1tween them. It is by means of the placenta nourishment of the growing offspring ined, it being a bond of union between o '8 ring and mother, the agent through which nourishment is conveyed from the blood of the mother. to the child. The placenta is also called the after-birth, from the fact that after the birth of the child it is separated and expelled from the womb. By the end of pregnancy it forms a disc-like mass, measuring 7i inches across, inch thick, and about 20 ounces in weight. Connected with it near the middle is the umbilical cord, by means of which the growing embryo is attached to the placenta. Running within the cord are two Arteries which carry the blood from the embryo to the pla centa. In the placenta the blood is distributed in large spaces, and comes into close communi cation with the blood of the mother, by means of which its purity and nourishing qualities are maintained. From the placenta the blood passes back along the cord in a vein to the em bryo, to which it gives up the requisite supply of material for continued life and growth.

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