THE CIRCULATION. 201 



the posterior part of the body, most of it is again by the 

 umbilical artery carried to the placenta, there to have its 

 oxygen supply renewed. 



At the moment of birth a number of changes occur. 

 The circulation of blood through the placenta is stopped, 

 and now with the first breath drawn into the lungs these 

 organs expand and allow the stream from the pulmonary 

 arteries to pass through them. Within a few hours the 

 opening from one auricle into the other begins to be closed 

 up, and the duct of Botallus becomes filled by depositions 

 of fat and connective tissue in its lumen. The stumps of 

 the umbilical artery and vein practically disappear, and the 

 circulation which is to be maintained throughout life is 

 established. It, however, not infrequently happens that 

 the opening in the auricular septum remains through life, 

 and in some cases even the duct of Botallus remains open. 

 Such individuals, must, of course, have their circulation 

 materially interfered with. The Eustachian valve in the 

 heart becomes almost obliterated, although even on an 

 adult heart traces of it, as well as the thin partition closing 

 the auricular septum, and the solid string, the remains of 

 the duct of Botallus, may still be readily seen. In this 

 rather remarkable way, without a break, the foetal circula- 

 tion becomes changed in a moment into the regular circu- 

 lation of the fully developed body. 



