. Kirkes' handbook of physiology . ble. These have been named the decidua vera, thedecidua basalis, and the decidua capsularis. In connection with these villous processes of the chorion, there are de-veloped depressions or crypts in the decidua vera, which correspond in shapeto the villi they are to lodge; and thus the chorionic villi become more orless embedded in the maternal structures. These uterine crypts, it is im- (I!) 1 DEVELOPMENT portant to note, arc not, as was once supposed, merely the open mouths ofthe uterine follicles. The Placenta. During these changes the deeper part of the mu
. Kirkes' handbook of physiology . ble. These have been named the decidua vera, thedecidua basalis, and the decidua capsularis. In connection with these villous processes of the chorion, there are de-veloped depressions or crypts in the decidua vera, which correspond in shapeto the villi they are to lodge; and thus the chorionic villi become more orless embedded in the maternal structures. These uterine crypts, it is im- (I!) 1 DEVELOPMENT portant to note, arc not, as was once supposed, merely the open mouths ofthe uterine follicles. The Placenta. During these changes the deeper part of the mucousmembrane of the uterus, at and near the region where the placenta isplaced, becomes hollowed out by sinuses, or cavernous spaces, which com-municate on the one hand with arteries and on the other with veins of theuterus. Into hese sinuses the villi of the chorion protrude, pushing the thin Unchanged layer Stratum spongiosumStratum compactum Placental vil. DecWua basalis Maternal vessel Primitive streakMesoderm Placental villus. Fig. so3. -Diagram of the Early Stage of Human Embryo in Relation to the Uterus.(Cunningham.) walls of the sinuses before them, and so come into intimate relation with theblood contained in them. There is no direct communication between the blood-vessels of the mother and those 0} the fetus; but the layer or layers of membraneintervening between the blood of the one and of the other offer no obstacle toa free interchange of matters between them by diffusion and osmosis. Thusthe villi of the chorion, containing fetal blood, are bathed or soaked in maternalblood contained in the uterine sinuses. The placenta, therefore, of the human subject is composed of a fetal partand a maternal part—the term placenta properly including all that entangle-ment of fetal villi and maternal sinuses, by means of which the blood of thefetus is enriched and purified after the fashion necessary for the proper growthand development of those parts which it is designed to no
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