. The elements of embryology. Chickens -- Embryos. 212 THE SIXTH DAY. [CHAP. near the end of incubation, when the chick begins to breathe the air in the air-chamber of the shell, and respiration is no longer carried on by the allantois. Blood then ceases to flow along the umbilical vessels; they become obliterated. The omphalo-mesaraic vein, which as the yolk becomes gradually absorbed proportionately diminishes in size and importance, comes to appear as a mere branch of the portal vein. The ductus venosus becomes closed, remaining often as a mere ligament; and hence the whole of the blood com
. The elements of embryology. Chickens -- Embryos. 212 THE SIXTH DAY. [CHAP. near the end of incubation, when the chick begins to breathe the air in the air-chamber of the shell, and respiration is no longer carried on by the allantois. Blood then ceases to flow along the umbilical vessels; they become obliterated. The omphalo-mesaraic vein, which as the yolk becomes gradually absorbed proportionately diminishes in size and importance, comes to appear as a mere branch of the portal vein. The ductus venosus becomes closed, remaining often as a mere ligament; and hence the whole of the blood coming through the portal vein flows into the substance of the liver, and so by the two hepatic veins into the vena cava (Fig. 64, HP). Previous to these changes one of the veins passing from the rectum into the vena cava has given off a branch which effects a junction with one of the mesenteric veins. This now forms a somewhat conspicuous connecting branch between the systems of the vena cava and the portal vein (Fig. 64, Co. V.). All three venae cavse now fall exclusively into the right auricle, and by the closure of the foramen ovale the blood Fig. 65. LCA. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Foster, M. (Michael), Sir, 1836-1907; Balfour, Francis M. (Francis Maitland), 1851-1882. London, Macmillan and co.
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Keywords: ., bookcentury1800, bookdecade1870, bookpublisherlondo, bookyear1874
