Final answer:
The primary venous drainage of the thigh is through the femoral vein, which receives blood from the deep femoral vein and the great saphenous vein. The popliteal vein, which forms from other veins including the anterior tibial vein, eventually becomes the femoral vein as it ascends.
Step-by-step explanation:
The venous drainage of the thigh primarily involves the femoral vein. The thigh's venous blood is collected by three main veins: the deep femoral vein, the great saphenous vein, and the femoral circumflex vein, all of which eventually drain into the femoral vein. The deep femoral vein handles the drainage of the deeper regions of the thigh, while the great saphenous vein is responsible for the superficial areas, prominently positioned on the medial side of the leg and thigh. The anterior tibial vein, which forms from the dorsal venous arch, drains an area near the tibialis anterior muscle and leads to the popliteal vein, not directly associated with the thigh's venous drainage.
The popliteal vein, formed by the convergence of the anterior and posterior tibial veins and the fibular vein, ascends to become the femoral vein as it passes behind the knee. Notably, the femoral vein is the key vessel that drains the upper leg and it goes on to become the external iliac vein as it crosses the body wall.