306 THE VASCULAR SYSTEM 



of the lungs with respiration determines the flow of a larger 

 quantity of blood to the lungs and causes an increased blood- 

 pressure within the pulmonary artery, which drags on the 

 ductus arteriosus. The latter is rendered oblique and soon 

 becomes a fibrous cord, termed the ligamentum arteriosum. 

 At the same time the foramen ovale closes, so that all direct 

 communication between the right and left sides of the heart is 

 cut off. 



After the ligature and division of the umbilical cord, the 

 blood in the umbilical vein, from the umbilicus to the left 

 branch of the portal vein, undergoes coagulation and the vessel 

 itself becomes converted into a fibrous cord, termed the liga- 

 mentum teres of the liver (p. 260). The ductus venosus 

 becomes transformed in a similar manner, but the cause of 

 this change is by no means clear. It has been suggested that 

 icterus neonatorum may be due to patency of the ductus 

 venosus. 



Congenital Anomalies of the Heart. Congenital 

 absence of the heart occurs in acardiac monsters, but the 

 condition is of little interest to the clinician as it is never 

 consistent with life. 



Dextro-cardia, or complete transposition of the heart, may be 

 associated with a similar transposition of the abdominal viscera, 

 and is always associated with transposition of the great vessels. 

 Patency of the foramen ovale may occur without producing 

 any characteristic signs. In these cases the opening, which is 

 slit-like in character, is usually of small size, and, as it is 

 provided with a valve-like arrangement, it possesses no clinical 

 significance. A patent foramen ovale may, however, be associ- 

 ated with other cardiac defects, such as imperfections of the 

 upper part of the interventricular septum and patency of the 

 ductus arteriosus. Although the child may be markedly 

 cyanosed and loud heart murmurs may be present, there is 

 seldom any enlargement of the left side of the heart and there 

 may be little increase in the cardiac dulness to the right of the 

 sternum. 



