Diseases of the heart and arterial system : designed to be a practical presentation of the subject for the use of students and practitioners of medicine . s. Stenosis of the pulmonary or aortic orifices may result fromthe more or less complete fusion of all three cusps (Fig. 78), andthis may even proceed to complete atresia. The fusion may bethe result of foetal endocarditis or developmental error. In theformer case the valve presents much the same appearance as after686 COXliKNITAIi IMSKASKS OF TIIK HEART 687 postnatal endocarditis. Vegetations may cover the cusps, projectinto the ventricle,
Diseases of the heart and arterial system : designed to be a practical presentation of the subject for the use of students and practitioners of medicine . s. Stenosis of the pulmonary or aortic orifices may result fromthe more or less complete fusion of all three cusps (Fig. 78), andthis may even proceed to complete atresia. The fusion may bethe result of foetal endocarditis or developmental error. In theformer case the valve presents much the same appearance as after686 COXliKNITAIi IMSKASKS OF TIIK HEART 687 postnatal endocarditis. Vegetations may cover the cusps, projectinto the ventricle, or fill the sinuses of Valsalva. At other times,however, the united valves may presenl no signs of endocarditis,being combined to form a tunnel, which may show signs of veryslight sclerosis. Stenosis or atresia of the nurieulo-ventricularorifices is of much less frequent occurrence than of the arterialopenings. In cither case the congenital disease is more frequenton the right side on account of the more frequent location of fetalendocarditis on that side. Pott says that for one congenital aorticdefect there are twenty-five pulmonary and Fig. 105.—Perforate Interventricular Pulmonary stenosis, already considered in a special chapter, isa by no means infrequent congenital anomaly. Aortic obstructionis far less frequently congenital. In either case if the obstruction 088 DISEASES OF THE HEART arises earlier than the eighth week of foetal life, it leads to animperfect formation of the interventricular sseptum. This is dueto the inequality of blood-pressure in the two ventricles occa-sioned by the stenosis, and the consequent passage of a stream ofblood from one to the other through the still imperfect saeptum,with each systole of the ventricles. This stream prevents theunion of the two fundaments of the saeptum, and in consequence,the imperfection is almost always situated at the pars membrana-cea, or point where the two embryonic fundaments fuse ().
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