The saphenous vein is located in the medial aspect of the lower limb, starting from the dorsal foot vein network, traveling up the medial aspect of the calf and thigh, and entering the common femoral vein in the groin. The saphenous vein is the longest vein in the human body, starting from the medial aspect of the dorsal foot vein network, passing over the anterior aspect of the inner ankle, traveling along the medial aspect of the calf, the medial aspect of the knee, the medial aspect of the thigh, and finally injecting itself into the common femoral vein in the inguinal region. Five branches converge before injection into the common femoral vein, including the external pubic vein, the superficial vein of the abdominal wall, the superficial vein of the spinous ilium, the lateral femoral vein, and the medial femoral (inner thigh) vein. If you find that the inner calf veins are tortuous and dilated, you need to consider the manifestation of saphenous vein varicose, which can be clearly diagnosed by ultrasound examination. The specific location of the saphenous vein can also be found by color ultrasound.