. An American text-book of obstetrics. For practitioners and students. e allantoic tissues become more prominent, the growthof the two systems proceeding in inverse order. The conversion of a portionof the vascular chorion into the fetal contribution of the placenta advancesthe importance of these vessels to that of the placental circulation, as firstrepresented by the two umbilical veins and the two umbilical arteries, thelatter the direct continuations of the intra-embryonic hypogastric , the two veins fuse within the allantoic stalk, thereby producing a singlevenous trunk whic
. An American text-book of obstetrics. For practitioners and students. e allantoic tissues become more prominent, the growthof the two systems proceeding in inverse order. The conversion of a portionof the vascular chorion into the fetal contribution of the placenta advancesthe importance of these vessels to that of the placental circulation, as firstrepresented by the two umbilical veins and the two umbilical arteries, thelatter the direct continuations of the intra-embryonic hypogastric , the two veins fuse within the allantoic stalk, thereby producing a singlevenous trunk which accompanies the arterial stems. Within the body of thefetus, however, the umbilical veins, which there remain separate, developunequally, the right suffering atrophy and finally disappearing, while the leftincreases in size and persists until birth as the important umbilical vein con-veying the blood to the liver. The Heart.—Coincidently with the formation of the primary extra-embry-onic blood-vessels within the vascular area, the heart early begins its develop-. Fig. 92.—Section of early embryo of rabbit (Piersol), showing two separate heart-tubes (H, H): e,primitive endothelium; cm, mesoderm forming cardiac wall; ec, ectoderm; en, entoderm; gf, folds pro-ducing ventral wall of gut-tract; hg, head-gut; a, a, primitive aorta ; n, neural canal. ment. The first trace of this important organ appears as a folding off andhollowing out of a limited mesodermic area on each side; the two heart-tubes VITELLINE CIECULATION. Plate i5. r,. r»„.
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectobstetrics, bookyear1
