CIRCULATION OF BLOOD IN THE FETUS 



733 



of the lining membrane of the heart, called the Eustachian valve, through the 

 foramen ovale into the left auricle and into the left ventricle, and out of this 

 into the aorta, and thence to all the body, but chiefly to the head and neck. 

 The blood of the right ventricle is sent out in small amount through the pul- 

 monary artery to the lungs, and thence to the left auricle, as in the adult, 

 but the greater part by far passes through a canal, the ductus arteriosus, 

 leading from the pulmonary artery into the aorta just below the origin of the 

 three great vessels which supply the upper parts of the body, and is distributed 



FIG. 505. Dissection of the Lower Half of the Female Mamma During the Period of 

 Lactation. . In the left-hand side of the dissected part the glandular lobes are exposed 

 and partially unravelled, and on the right-hand side the glandular substance has been 

 removed to show the reticular loculi of the connective tissue in which the glandular lobules 

 are placed, i, Upper part of the mammilla or nipple; 2, areola; 3, subcutaneous masses 

 of fat; 4, reticular loculi of the connective tissue which support the glandular substance 

 and contain the fatty masses; 5, one of three lactiferous ducts shown passing toward the 

 mammilla, where they open; 6, one of the sinus lactei or reservoirs; 7, some of the glandular 

 lobules which have been unravelled; 7', others massed together. (Luschka.) 



to the trunk and lower parts of the body. A large portion passes out by 

 way of the two umbilical arteries to the placenta. From the placenta it is 

 returned by the umbilical vein to the under surface of the liver, from which 

 the description started. 



After birth the foramen ovale, the ductus arteriosus, and ductus venosus 

 all close, and the umbilical vessels are tied off, so that the two streams of 

 blood which arrive at the right auricle by the superior and inferior vena cava, 

 respectively, thenceforth mingle in this cavity of the heart, and pass into the 

 right ventricle, by way of the pulmonary artery to the lungs, and through 



