Chap. XI] THE VASCULAR SYSTEM 199 



as Scarpa's triangle.^ In this situation the beating of the artery 

 may be felt, and the circulation through the vessel may be most 

 easily controlled by pressure. 



The popUteal artery, continuous with the femoral, is placed at 

 the back of the knee ; just below the knee-joint it divides into 

 the posterior tibial and anterior tibial arteries. 



The posterior tibial artery lies along the back of the leg, and 

 extends from the bifurcation of the popliteal to the ankle, where it 

 divides into the internal and external plantar arteries. 



The peroneal artery is a large branch given off by the posterior 

 tibial just about an inch (25 mm.) below the bifurcation of the 

 popliteal. 



The anterior tibial artery, the smaller of the two divisions of 

 the popliteal trunk, extends along the front of the leg to the bend 

 of the ankle, whence it is prolonged into the foot under the name of 

 the dorsalis pedis artery. This unites with the external and 

 internal plantar arteries to form the plantar arch which supplies 

 blood to the foot.^ 



VEINS 



The arteries begin as large trunks, which gradually become 

 smaller and smaller until they end in the small capillary tubes, 

 while the veins begin as small branches which at first are scarcely 

 distinguishable from the capillaries, and unite to form larger and 

 larger vessels. They differ from the arteries in their larger capacity, 

 greater number, thinner walls, and in the presence of valves which 

 prevent backward circulation. The veins may be divided into 

 two sets — a superficial and a deep set. 



The superficial set — are found immediately beneath the skin. 



The deep set — accompany the arteries and are usually called 

 by the same names. 



Sometimes two deep veins accompany an artery, and are then 

 called venae comites, or companion veins, or one single trunk may 

 accompany an artery, and then be known as the vena comes of 

 that artery. The superficial and the deep veins have very frequent 



1 Scarpa's triangle is a name given to a triangular space situated on the upper, 

 anterior, and inner surface of the thigh. It is bounded above by Poupart's ligament, 

 on the outer side by the sartorius muscle, and on the inner side by the adductor. 



2 Drawing t^ie outline of the aorta with its branches as an arterial tree will greatly 

 aid the student in mastering the arterial distribution. 



