34 ANATOMY IN A NUTSHELL. 



The umbilical win passes from the placenta to the under surface of the 

 liver going through the umbilicus and the free margin of the suspensory liga- 

 ment. At the transverse fissure this vein divides into two branches. A large 

 <»ne which is joined by the portal vein and enters the right lobe of the liver. 

 A smaller one the ductus venosus — joins the left hepatic vein at its junction 

 with the interim' vena cava. Before it divides the umbilical vein gives branches 

 to the left, quadrate, and Spigelian lobes. 



The pure blood coming from the placenta in the umbilical vein reaches the 

 interim- vena cava in three ways; 



1. A small quantity via ductus venosus into the hepatic veins and in- 

 ferior vena cava. 



2. Smne enters the liver directly and then passes through the hepatic veins. 

 :!. Most of it passes through the liver with the portal venous blood and 



then through the hepatic veins. 



In the inferior vena cava all this blood mixes with venous blood from the 

 lower extremities and abdominal wall. It now enters the right auricle from 

 which it passes to the lefl auricle through the foramen ovale being guided by 

 the Eustachian valve. In the lefl auricle it mixes with the blood which comes 

 from the pulmonary veins, which is venous and a small amount. It now passes 

 through the auriculo-ventricular opening into the left ventricle, from here 

 through the aorta to the head and upper extremity, some passing into the de- 

 scending aorta. The venous blood from the upper extremities and head de- 

 scends in the superior vena cava into the right auricle of the heart and here it 

 mixes with a small pari of the blood from the inferior vena cava. From here it 

 passes through the auriculo-ventricular opening to the right ventricle. A 

 systole sends the blood from the right ventricle into the pulmonary artery, a 

 small pari of the blood passing into the lungs and the remainder goes through 

 the ductus arteriosus to the descending aorta, where it mixes with blood from 

 the left ventricle after it has passed through the arch of the aorta. Most of 



the lil 1 in the descending aoria passes through the umbilicus to the placenta, 



and the rest to the lower limbs and viscera. 



The adult gets nourishment from the alimentary canal and oxygen from the 

 lungs. The placenta acts both as a nutritive and a respiratory organ. The 

 liver, the head, and the upper extremities are large in the fetus because the 

 purely arterial blood passes to these organs. The other viscera and the lower 

 extremities are small because the blood which passes to them is practically 

 venous. 



At birth the placental circulation stops, while the pulmonary circulation 

 is increased and the lungs expand. The foramen ovale closes about the tenth 

 day and the valvular folds adhers to its margin. As said before, the foramen 

 ovale remains open throughoul life in one case ou1 of five. The umbilical 

 arteries become obliterated beyond the bladder in from two to five days. The 

 umbilical vein and ductus venosus dose about thesame time as the umbili- 

 cal arteries. The ductus arteriosus closes in from four to ten days. 



\ plexus i- a net-work. (Plate VI.) The Brachial Plexus is a net work of 

 nerves situated in the axilla. It is called brachial because its branches supply 



