. 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. is usually open, and the interventricular steptum issometimes incom])lete. The pulmonary artery is always nar-rowed, and there may be atresia of this vessel. The ductus arterio-sus is generally oi)en, yet is in some cases found closed. Veryrarely the stenosis is caused by constriction of the right conusarteriosus, in which event this may appear like a third ventricle,and both the interventricular and interauricular septa are defect-ive, the
. 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. is usually open, and the interventricular steptum issometimes incom])lete. The pulmonary artery is always nar-rowed, and there may be atresia of this vessel. The ductus arterio-sus is generally oi)en, yet is in some cases found closed. Veryrarely the stenosis is caused by constriction of the right conusarteriosus, in which event this may appear like a third ventricle,and both the interventricular and interauricular septa are defect-ive, the pulmonary artery is narrowed or even occluded, and theductus Botalli remains pervious. In other cases there are various errors of development, as trans-position of the aorta and pulmonary artery, or their origin fromone common tnmk; a blending of the two ventricles into one com- PULMO^fARY STENOSIS 379 mon cavity with but one instead of two auricles; or one ventricleand two auricles, or but one auricle and two ventricles. It is not always easy to determine post mortem whether a givencase belongs to the congenital or the acquired category. In well-. **.. Fig. 78.—Heart of a Boy, showing Congenital Stenosis of the Pulmonary in collection of Dr. Gustav Filtterer. marked specimens, like Fengers, or in such as show striking ab-normalities of development the decision may be easy; but in casespresenting some of the characteristics of both forms the exactnature must be left in doubt. Aside from the evidences of recent endocarditis it is the condi-tion of the pulmonary artery upon which pathologists rely for thedetermination of the intra- or extra-uterine development of the 380 DISEASES OF THE HEART lesion. Dilatation of this vessel makes strongly for the acquiredform, while narrowing of the artery points to the foetal origin ofthe disease. Etiology.—The congenital form can be dismissed with thestatement that it results either from intra-uterine endocarditis ormyoca
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