A treatise on the science and practice of midwifery . ut directly into the right ventricle,and from thence into the pulmonary arteries, and the ductus arte-riosus soon collapses and becomes impervious. The mass of blood inthe descending aorta no longer finds its way into the hypogastricarteries, but passes into the lower extremities, and the adult circula-tion is established. Changes after Birth.—The changes which take place in the tempo-rary vascular arrangements of the foetus, prior to their complete dis-appearance, are of some practical interest. The ductus arteriosus,as has been said, coll
A treatise on the science and practice of midwifery . ut directly into the right ventricle,and from thence into the pulmonary arteries, and the ductus arte-riosus soon collapses and becomes impervious. The mass of blood inthe descending aorta no longer finds its way into the hypogastricarteries, but passes into the lower extremities, and the adult circula-tion is established. Changes after Birth.—The changes which take place in the tempo-rary vascular arrangements of the foetus, prior to their complete dis-appearance, are of some practical interest. The ductus arteriosus,as has been said, collapses, chiefly because the mass of blood is drawnto the lungs, and partly, perhaps, by its own inherent contractility. Itswalls are found to be thickened, and its canal closes, first in the centre,and subsequently at its extremities, its aortic end remaining longer per-vious on account of the greater pressure of blood from the left side ofthe heart (Fig. 67). Practical closure occurs within a few days after ANATOMY AND PHYSIOLOGY OF THE FCETUS 121. Diagram of Heart of Infant.(After Dalton.) 1. Aorta. 2. Pulmonary , 3. Pulmonary branches. 4. Duc-tus arteriosus becoming obliterated. birth, although Flourens states that it is Fig. 67. not completely obliterated until eighteenmonths or two years have Ac-cording to Schroeder, its walls unite with-out the formation of any thrombus. Theforamen ovale is soon closed by its valve,which contracts adhesion with the edgesof the aperture, so as effectually to occludeit. Sometimes however, a small canal ofcommunication between the two auriclesmay remain pervious for many months, oreven a year and more, without, however,any admixture of blood occurring. Apermanently patulous condition of thisaperture, however, sometimes exists,giving rise to the disease known ascyanosis. The umbilical arteries and veins, and the ductus venosus soon alsobecome impermeable, in consequence of concentric hypertrophy oftheir tissues and collapse
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