. Embryology. Embryology; Embryology; genealogy. FORMATION OF BLOOD VESSELS AND THE HEART 177 tubes develop and fuse to form the lining of the heart—the endocardium—as illustrated in Figure 104. The muscular coat of the heart differentiates from the splanchnic mesoderm, which fuses around the endocardium. This heart begins to twitch after about 29 hours of incubation, even before the blood vessels have formed a complete circulatory pathway. The heart continues to beat, and at 38 hours circulation is established and the blood follows the pathway indicated in Figures 101 and 105. At this early p
. Embryology. Embryology; Embryology; genealogy. FORMATION OF BLOOD VESSELS AND THE HEART 177 tubes develop and fuse to form the lining of the heart—the endocardium—as illustrated in Figure 104. The muscular coat of the heart differentiates from the splanchnic mesoderm, which fuses around the endocardium. This heart begins to twitch after about 29 hours of incubation, even before the blood vessels have formed a complete circulatory pathway. The heart continues to beat, and at 38 hours circulation is established and the blood follows the pathway indicated in Figures 101 and 105. At this early period the heart does not have any nervous supply, and the rhythmic pulsations are controlled entirely within the heart itself. Even if the heart is removed from the embryo and cultivated in vitro it continues to contract rhythmically. Tissues from the embryonic heart are very viable and can be grown in tissue culture. This primitive circulatory system undergoes drastic changes during de- velopment. The changes, in general, follow the course of the changes which occurred in the evolution of the species to which the embryo belongs. Thus, in the early chick embryo we find a two-chambered heart, aortic arches, and a cardinal venous system, all of which are reminiscent of the circulatory system in fishes. Figures 102 and 106 show this striking resemblance. The Fig. 105. The structure of the circulatory system just after the blood begins to flow in a complete circuit. The vitelline veins have joined up with the endocardium of the heart. Aortic arches connect the heart with the dorsal aorta. The vitelline arteries join the dorsal aorta. A very complicated network of blood vessels, which develops in the area vasculosa, connects the vitelline arteries with the vi- telline veins. The flow of blood is shown by Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustra
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Keywords: ., boo, bookcentury1900, booksubjectembryology, booksubjectgenealogy
