. Analysis of development. Embryology; Embryology. First Aortic Arch Ventricle Atrial Primordia v • (unfused) (fused) Future Sinus Level Fig. 161. Progressive fusion of paired primordia during morphogenesis of chick heart. A, at 9-somite (± 29 hour) stage, when first contractions appear; B, at 16-somite {± 38 hour) stage, when blood circula- tion begins. (Redrawn after Patten and Kramer, '33.). ences in the embryonic tissues (, Triturus taeniatus and T. cristatus). Experiments by Goss ('35) show that some totipotency exists in the primordium of the mammalian heart. He found that double hea
. Analysis of development. Embryology; Embryology. First Aortic Arch Ventricle Atrial Primordia v • (unfused) (fused) Future Sinus Level Fig. 161. Progressive fusion of paired primordia during morphogenesis of chick heart. A, at 9-somite (± 29 hour) stage, when first contractions appear; B, at 16-somite {± 38 hour) stage, when blood circula- tion begins. (Redrawn after Patten and Kramer, '33.). ences in the embryonic tissues (, Triturus taeniatus and T. cristatus). Experiments by Goss ('35) show that some totipotency exists in the primordium of the mammalian heart. He found that double hearts develop in 9-day-old rat embryos in hanging drop cultures when the lateral primordia are prevented from uniting. The lateral rudiments self-differentiate beyond the stage when they luiite in normal de- velopment. Available experimental methods do not maintain the growth of separated mammalian heart primordia for sufficient time to show whether a half can develop a fully differentiated mammalian heart with two atria and two ventricles. When double hearts develop from sepa- rate bilateral primordia, the left heart has be considered in relation to asjonmetry of entodermal derivatives. Formation of the "Tubular" Heart and Functional Differentiation. Fusion of the bi- lateral heart primordia occurs in a cephalo- caudal sequence, with formation of the bulboventricular region first and the sinus venosus last. Space does not permit reference to all of the studies which have established this point for amphibians, birds and mam- mals, including man (Davis, '27). Likewise, it has been demonstrated that functional dif- ferentiation progresses in a cephalocaudal direction. Sabin ('20) and Johnstone ('25) appear to have been the first to note that the earliest contractions in the chick heart begin in the ventricle. Using a cinemato- graphic method, Patten and Kramer ('33). Please note that these images are extracted from scanned page images that may have been digitally enha
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Keywords: ., bookcentury1900, bookpublisherphiladelphi, booksubjectembryology
