Figure. Left gracilis, anterior view.
A long, thin muscle, gracilis, as its name implies, is situated on the medial side of the thigh. Gracilis is the most superficial of the adductor group. Its upper attachment is to the front of the body of the pubis and its inferior ramus, just encroaching onto the ramus of the ischium. As it descends between semimembranosus posteriorly and sartorius anteriorly, gracilis develops a fusiform-shaped belly at about its middle. It becomes tendinous above the knee and crosses the joint before expanding to attach to a short vertical line on the upper part of the medial surface of the shaft of the tibia. This attachment is above that of semitendinosus and behind and blends with that of sartorius. Bursae separate the tendon of gracilis from those of sartorius and semitendinosus.
Figure. Muscle attachments to the outer surface of the pubis, ischium and obturator membrane.
By the anterior division of the obturator nerve (root value L2 and 3). The skin covering this area is innervated by roots L2 and 3; the upper part by the obturator nerve and the lower part by the femoral nerve.
Although gracilis is situated with the adductor group of muscles, its action of adduction at the hip joint is not so important as its action on the knee. It is mainly a flexor of the knee, but with the knee in a semiflexed position it aids medial rotation of the leg on the thigh.
As a flexor of the knee, gracilis helps the hamstrings in simple flexion activities, such as the beginning of the swing phase in walking when the knee needs to be flexed. It also
helps when strong flexion is required, as when pulling the body forward on the sliding seat of a rowing boat. In horse riding, gracilis is used in all its actions. When the rider is gripping the horse, gracilis helps the adductor muscles, whilst at the same time helping to control the flexed knee.
In the sitting position with the medial aspect of the foot against a solid object, such as the leg of a table, or when the toes are pointing towards the midline, the tendon can be felt on the posteromedial aspect of the knee joint, being the upper of the two obvious tendons. If traced upwards, the muscle belly can be palpated and traced to its attachment on the front of the pubic body.