A system of obstetrics . of the throat (Fig. 113), and the whole organ becomessomewhat horseshoe-shaped. As this change in form occurs, the prim-itive posterior or venous end of the heart becomes pushed dorsally (A, 2, Fig. 112), in reference to the ventricular portion, V: from it the DEVELOPMENT OF ORGANS AND SYSTEMS. 173 auricles (3, 4, Fig. 112) grow out on each side. About the fourth orfifth week iu the human embryo the septum between the ventriclescommences to develop (5, Fig. 112). A little later the portion of theaortic bulb nearest the ventricles becomes divided by a cross-septumwhich
A system of obstetrics . of the throat (Fig. 113), and the whole organ becomessomewhat horseshoe-shaped. As this change in form occurs, the prim-itive posterior or venous end of the heart becomes pushed dorsally (A, 2, Fig. 112), in reference to the ventricular portion, V: from it the DEVELOPMENT OF ORGANS AND SYSTEMS. 173 auricles (3, 4, Fig. 112) grow out on each side. About the fourth orfifth week iu the human embryo the septum between the ventriclescommences to develop (5, Fig. 112). A little later the portion of theaortic bulb nearest the ventricles becomes divided by a cross-septumwhich ultimately fuses with the ventricular partition; it separates theroot of the pulmonary artery from the aorta, but until after birth thetwo vessels meet at a short distance from the heart (B, Fig. 112,7). Theauricular septum appears later (eighth week) than the ventricular, andremains incomplete until after birth, so as to allow the two auricles tocommunicate through the foramen ovale. The veuous sinus has mean- Fig. To Illustrate the Development of the Heart (after Landois): 1, heart after its two primitivetubes have coalesced; 6, aortic bulb; o, first pair of aortic arches; v, venous end of heart;_. heart curved so as to resemble a horseshoe; a and b, as before; A, commencing auricles;on these the commencing auricular appendages, o and o, are shown; T, commencing ven-tricles: 1 shows the commencing division of the aortic bulb into aorta and pulmonary artery; 5 shows the embryonic heart after the dorsal auricular wall has been cut away, so as toexpose the cavities of the ventricles and the septum which has developed between them ; 6 indicates the direction of the venous blood, from the superior cava, Cs, into the right ven-tricle, and from the inferior cava, Ci, into the left auricle; 7, heart of foetus at term; E,right, L, left ventricle; a, aorta and (cc, c, s) the brandies from its arch; B, ductus arteri-osus (ductus Botalli); p, pulmonary artery, and 1 and 2, its smal
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectobstetrics, bookyear1
