THE DEVELOPMENT OF THE VASCULAR SYSTEM 



249 



branch between its point of origin and the anastomosis atrophies, leaving 

 only a small vessel which goes to the biceps muscle. The second branch 

 and the remaining part of the first branch together form the radial artery 

 (Fig. 227) (McMurrich). 



In the lower extremity the primary artery is a continuation of the common 

 iliac which, in turn, is a branch of the aorta. This primary vessel, the sciatic 

 artery, passes distally as far as the ankle. Below the knee it gives off a short 

 branch which corresponds to the proximal part of the anterior tibial artery. 

 Just above the ankle it gives off another branch which corresponds to the 

 distal part of the anterior tibial. As will be seen, these two parts join at a 

 later period to form a continuous vessel. At this early stage the external 



Brachial artei 1" 



Superficial radia* artery- 



Median artery 

 Interosseous artery 



Ulnar artery y 



A 



Brachial artery 



B 



.... Median artery 



-- Interosseous artery 

 ---- Ulnar artery 



Radial artery 



FIG. 227. Diagrams showing (A) an early and (5) a late stage in the development 

 of the arteries of the upper extremity. McMurrich. 



iliac artery is but a small branch of the common iliac; but it gradually in- 

 creases in size, extends farther distally in the thigh as the femoral artery 

 and unites with the sciatic near the knee. Just proximal to its union with 

 the sciatic it gives off a branch which extends distally along the inner side 

 of the leg to the plantar surface of the foot, where it gives off the digital 

 branches. This vessel is the saphenous artery in the embryo, and disappears 

 in part during further development. From this time on, the femoral and its 

 direct continuation, the popliteal, increase in size; and at the same time the 

 sciatic loses its primary connection and becomes much reduced to form the 

 inferior gluteal artery. The direct continuation of the sciatic in the leg, which 

 is now the direct continuation of the popliteal, becomes reduced to form the 



