The nerve to the quadratus femoris (L4 to S1) and the nerve to the obturator internus (L5 to S2) are small motor nerves that originate from the sacral plexus. Both nerves pass through the greater sciatic foramen inferior to the piriformis muscle and enter the gluteal region (Fig. 6.36 and Table 6.1):
The nerve to the obturator internus supplies the gemellus superior muscle in the gluteal region and then loops around the ischial spine and enters the perineum through the lesser sciatic foramen to penetrate the perineal surface of the obturator internus muscle.
The nerve to the quadratus femoris supplies the gemellus inferior and quadratus femoris muscles.
Posterior cutaneous nerve of thigh
The posterior cutaneous nerve of the thigh is formed by contributions from S1 to S3 and leaves the pelvic cavity through the greater sciatic foramen inferior to the piriformis muscle (Fig. 6.36 and Table 6.1). It passes vertically through the gluteal region deep to the gluteus maximus and enters the posterior thigh and innervates: a longitudinal band of skin over the posterior aspect of the thigh that continues into the upper leg, and skin over the gluteal fold, over the upper medial part of the thigh and in the adjacent regions of the perineum.
The perforating cutaneous nerve is a small sensory nerve formed by contributions from S2 and S3. It leaves the pelvic cavity by penetrating directly through the sacrotuberous ligament (Fig. 6.36 and Table 6.1) and passes inferiorly around the lower border of the gluteus maximus where it overlaps with the posterior cutaneous nerve of the thigh in innervating skin over the medial aspect of the gluteal fold.
The major artery supplying the lower limb is the femoral artery (Fig. 6.37), which is the continuation of the external iliac artery in the abdomen. The external iliac artery becomes the femoral artery as the vessel passes under the inguinal ligament to enter the femoral triangle in the anterior aspect of the thigh. Branches supply most of the thigh and all of the leg and foot.
the obturator artery
Other vessels supplying parts of the lower limb include the superior and inferior gluteal arteries and the obturator artery (Fig. 6.37).
The superior and inferior gluteal arteries originate in the pelvic cavity as branches of the internal iliac artery (see Chapter 5, pp. 489–492) and supply the gluteal region. The superior gluteal artery leaves the pelvis through the greater sciatic foramen above the piriformis muscle, and the inferior gluteal artery leaves through the same foramen but below the piriformis muscle.
The obturator artery is also a branch of the internal iliac artery in the pelvic cavity (see Chapter 5, pp. 490–491) and passes through the obturator canal to enter and supply the medial compartment of the thigh.
Branches of the femoral, inferior gluteal, superior gluteal, and obturator arteries, together with branches from the internal pudendal artery of the perineum, interconnect to form an anastomotic network in the upper thigh and gluteal region. The presence of these anastomotic channels may provide collateral circulation when one of the vessels is interrupted.
Veins draining the lower limb form superficial and deep groups.
The deep veins generally follow the arteries (femoral, superior gluteal, inferior gluteal, and obturator). The major deep vein draining the limb is the femoral vein (Fig. 6.38). It becomes the external iliac vein when it passes under the inguinal ligament to enter the abdomen.
The superficial veins are in the subcutaneous connective tissue and are interconnected with and ultimately drain into the deep veins. The superficial veins form two major channels—the great saphenous vein and the small saphenous vein. Both veins originate from a dorsal venous arch in the foot: