2IO 



ANATOMY AND PHYSIOLOGY 



the umbilical vein. After circulating in the body of the child 

 it is returned to the placenta by two special vessels called the 

 umbilical arteries, branches of the hypogastrics. (They shrink 

 to fibrous cords after birth, which may be seen on the interior 

 surface of the abdominal wall.) 



During intrauterine life the lungs do not contain air, therefore, 

 the interchange of oxygen and carbon dioxid in the blood must be 

 accomplished elsewhere. This also is brought about by means of 

 the placental vessels. 



Opening closed by 

 tricuspid valve 

 Foramen ovale 



Coronary sinus 



Location of Eu- 



stachian valve 



FIG. 147. INFANT'S HEART. 

 Showing interior of right atrium. (Holden.) 



The plan of fetal circulation requires still other special pro- 

 vision, namely: 



The foramen ovale. An opening in the septum between the 

 two atria (Fig. 147). It closes after birth. 



The Eustachian valve. A fold of endocardium in the R. 

 atrium (so placed as to direct the blood from the inferior vena 

 cava through the foramen ovale). This remains after birth. 



The ductus arteriosus. A short trunk (1/2 inch long) which 

 connects the pulmonary artery with the arch of the aorta. This 

 shrinks to a cord after birth. 



The course of the blood is as follows: Arterial blood is brought 

 through the umbilical vein which enters the body at the umbilicus, 

 runs upward under the liver (giving branches to that organ) and 

 terminates by opening into the inferior vena cava, just below 

 the diaphragm. This blood flows at once into the right atrium 

 of the heart, where it is guided by the Eustachian valve through 



