. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. 234 THE FORMATION OF THE HEART Si Sz. When the absorption of the sinus venosus into the wall of the right atrium has proceeded so far that the veins communicate directly with the atrium, the vena cava superior opens into it at the upper part of the dorsal wall, the vena cava inferior more laterally, and below this is the smaller opening of the coronary sinus. The upper portion of the right lip of the fold which originally surrounded the opening of the sinus venosus, together with the septum s
. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. 234 THE FORMATION OF THE HEART Si Sz. When the absorption of the sinus venosus into the wall of the right atrium has proceeded so far that the veins communicate directly with the atrium, the vena cava superior opens into it at the upper part of the dorsal wall, the vena cava inferior more laterally, and below this is the smaller opening of the coronary sinus. The upper portion of the right lip of the fold which originally surrounded the opening of the sinus venosus, together with the septum spurium, gradually disappears; the lower portion persists, however, and forms (i) the Eustachian valve (Fig. 141, Ve), guarding the opening of the inferior cava and directing the blood entering by it toward the foramen ovale, and (2) the Thebesian valve, which guards the open- ing of the coronary sinus. At first no Fig. 141.—Heart of Embryo veins communicate with the left atrium, OF CM. FROM WHICH HALF , 111 c t i 1 of the Right Auricle has but on the development of the lungs and been Removed. the establishment of their vessels, the fo, Foramen ovale; pa, pul- , . .,, monary artery; Su septum pri- pulmonary veins make connection with mum; S2,_ septum secundum; jt TwQ yejns arise from each lung an(J ba, systemic aorta; V, right ven- ° tricle; vd and vcs, inferior and as they pass toward the heart they unite superior venae cavae; Ve, Eusta- ,-, i r „ j • chfan valve. in pairs, the two vessels so formed again uniting to form a single short trunk which opens into the upper part of the atrium (Fig. 142, Vep). As is the case with the right atrium and the sinus venosus, the expansion of the left atrium brings about the absorption of the short single trunk into its walls, and, the expansion continuing, the two vessels are also absorbed, so that eventually the four primary veins open independ- ently into the atrium. While the atrial septa have been developing there has appear
Size: 1457px × 1716px
Photo credit: © Central Historic Books / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookautho, bookcentury1900, bookdecade1910, booksubjectembryology
