I. Arteries of the lower extremity (a) Femoral artery The femoral artery is the main trunk of the arteries of the lower extremity, extending from the external iliac artery, through the deep surface of the midpoint of the groin, and through the femoral triangle into the internal collecting duct. Slightly below the inguinal ligament, the femoral artery is superficially located and its pulsation can be palpated in vivo, where it can be compressed to stop bleeding when the lower extremity bleeds. The femoral artery divides into the superficial femoral artery and the deep femoral artery in the limb. The superficial femoral artery is the primary blood supply artery to the lower extremity. The deep femoral artery is the largest branch of the femoral artery, which in turn divides into the lateral and medial rotor femoral arteries. When the superficial femoral artery is occluded and traumatized, the blood supply to the limb mainly relies on the deep femoral artery and its collateral circulation. The femoral artery is the most commonly used and dissected artery in clinical practice, which includes angiography, endoluminal molding of arteries in various areas, vascular stenting, placement of stents with membranes, and lower extremity vascular surgery. It is also used clinically for femoral artery puncture and for compression to stop bleeding in emergency situations. (ii) N artery It is the direct continuation of the femoral artery in the N fossa and is located deeper. The N artery is the hub of the vascular connection between the thigh and the calf, and there is little collateral circulation in this area, so when the thrombus of the cardiac appendage is dislodged, it often blocks the artery and causes acute arterial embolism. Since the N artery is the hub of the arterial vascular connection between the thigh and calf, it must be repaired and reconstructed after injury. (C) Anterior tibial artery and posterior tibial artery After passing through the N fossa, the N artery divides into three main vessels in the lower leg: anterior tibial, posterior tibial and peroneal arteries. In the lower corner of the N fossa, the N artery usually divides into two terminal branches, the anterior tibial artery and the posterior tibial artery. The main trunk of the posterior tibial artery enters the plantar aspect of the foot via the posterior aspect of the medial ankle and emanates from the peroneal artery at its origin. In cases of acute and chronic ischemia of the limb, the three arteries are usually the anastomoses of the arterial arch and venous arterialization of the lower limb, and when one of the three arteries is patent, it means that the ischemic limb can survive, recover, and be relieved. (iv) Dorsalis pedis artery The anterior tibial artery migrates into the dorsalis pedis artery. It runs between the medial thumb extensor tendon and the long toe extensor tendon on the dorsal side of the foot, through the 1st and 2nd metatarsal gaps to the sole of the foot. It is palpable at the anterior aspect of the ankle joint, at the midpoint of the internal and external ankle line, and lateral to the extensor hallucis longus tendon. Bleeding into the foot can be stopped by compressing the dorsalis pedis artery here. In clinical practice, the strength of the pulsation of the dorsalis pedis artery and posterior tibial artery is often used to check the blood supply to the extremity after arterial reconstruction of the lower extremity. The lower extremity veins are rich in centripetal unidirectional opening valves, which prevent the venous blood from flowing backwards and ensure the unidirectional return of venous blood from the bottom to the top and from the superficial to the deep. The veins of the lower extremity are divided into superficial and deep groups, and the superficial veins and deep veins are connected by many traffic branches, which finally converge into the deep veins. (a) Superficial veins mainly include saphenous vein and small saphenous vein. The saphenous vein starts from the medial end of the dorsal arch of the foot on the medial side of the foot, and travels up along the medial calf and anterior medial thigh via the front of the inner ankle to the lower part of the pubic symphysis and enters the deep surface and injects into the femoral vein. The saphenous vein is superficially located in front of the medial ankle and is prone to varicose veins. It is also commonly used clinically for venipuncture or incisional infusion. It is commonly used in vascular surgery as a material for vascular arches or vascular patches. The small saphenous vein starts at the lateral edge of the foot from the lateral end of the dorsal foot vein arch and travels up the back of the external ankle to the N fossa, where it is injected into the N vein through the deep fascia. (ii) The deep veins of the foot and lower leg are accompanied by the eponymous artery, both of which are two in number. The anterior and posterior tibial veins converge to form the N vein. Below the knee two veins accompany each artery and travel up to the N fossa to form a single N vein. The femoral vein, which passes through the tensor fasciae, accompanies the femoral artery superiorly, initially on its lateral side, then turns medially and reaches the deep surface of the inguinal ligament and moves into the external iliac vein. The femoral vein collects all the superficial and deep venous blood of the lower extremities and finally flows to the heart. As shown in the following pathway: superficial veins of the lower extremity → anterior and posterior tibial veins → N vein → femoral vein → external iliac vein → common iliac vein → right atrium → right ventricle. In clinical practice, the thrombus dislodged by deep vein thrombosis in the lower extremities also follows the above path and finally embeds in the pulmonary artery, causing pulmonary embolism.