264 Human Physiology. 



organs; their extreme minuteness and rapid development into 

 all the complexities of our wondrous organisation, constitute a 

 series of mysteries. But the mode of foetal existence is strangely 

 different from that of the infant from the moment it comes into 

 the world The foetus cannot breathe. Its lungs are useless 

 no blood is thrown into them except what is necessary for their 

 growth, and no air penetrates them, for the foetus swims in a 

 liquid. The foetal heart has an open communication between 

 the two auricles which is closed at birth. The blood of the 

 infant gets its supply of oxygen from the blood of the mother 

 by means of the placenta, or afterbirth. The lungs of the 

 mother breathe for herself and her offspring during pregnancy, 

 so that pure air is then more than ever needed. The blood of 

 the child, fed and punned by that of the mother, passes from 

 the placenta through the umbilical vein to its liver, and thence 

 into the right auricle of the heart, and from that into the left 

 auricle through the foetal opening between them, and then to 

 the left ventricle, and is expelled into the arteries which supply 

 the head and upper extremities with the purest blood for their 

 more rapid development From the head and arms the blood 

 returns into the right auricle, from which it passes to the right 

 ventricle. In the adult it would now pass into the lungs, but 

 in the foetus it is carried by a special artery, afterwards oblitera- 

 ted, into the descending aorta, and sent partly to the lower 

 extremities, and partly to the placenta, to be purified by contact, 

 through thin membranes, with the blood of the mother. 



Here we have a special machinery, an opening in the heart 

 which is closed at birth, lungs solid and useless, arteries and 

 veins most important in the foetus, but at birth obliterated, and 

 an organ expelled at birth after the infant, which in its foetal 

 life performs the function of both stomach and lungs, furnishing 

 the matter of blood, and also the oxygen for its purification and 

 vivification. 



The average duration of gestation or foetal life is nine months, 



