The sartorius muscle is the longest muscle in the entire human body. It is a long, thin, band-like muscle found in the anterior region of the thigh. The sartorius functions as an important flexor and rotator of the thigh at the hip joint.
The sartorius muscle arises from the anterior superior iliac spine on the lateral edge of the hip bone. From the lateral hip, it descends obliquely across the hip joint and thigh, running medially and inferiorly toward the medial edge of the knee. At the knee, the sartorius turns more laterally as it descends to insert on the medial side of the tibia in the lower leg.
The sartorius muscle is so long that it crosses and acts upon both the hip and knee joints. Acting on the hip joint, the sartorius works as a flexor, abductor, and lateral rotator of the thigh with the assistance of the other major muscles of the hip. At the knee joint the sartorius helps to flex the leg. Combining all of these functions into one movement, the sartorius pulls the foot and ankle toward knee of the opposite leg. The action of the sartorius is used in many situations, such as crossing the legs so that the ankle rests on the knee of the opposite leg; sitting cross-legged; or looking at the sole of one’s foot. In fact, the name sartorius (from the Latin word for “tailor”) and its nickname, the “tailor’s muscle,” are derived from the common motion of tailors crossing their legs to sit while working.