(2.27)

Now we’ll look at the two gluteal nerves, the superior and the inferior, and at the largest nerve of the lower extremity, the sciatic nerve, which supplies the posterior thigh muscles, and also almost everything below the knee. The gluteal and sciatic nerves arise from the sacral plexus.

Here’s the sacral plexus. It’s formed by the anterior rami of L4 and 5, and S1,2 and 3. The sacral plexus overlies the piriformis muscle.

This is the sciatic nerve. It arises from L4 through S3. This is the superior gluteal nerve. The inferior gluteal nerve arises out of sight behind the sciatic nerve. All three nerves leave the pelvis through the greater sciatic foramen. To see where they come out, we’ll go round to the back, and remove gluteus maximus.

Here, the vessels have been removed to simplify the picture. Here’s piriformis. Here’s the sciatic nerve, here’s the inferior gluteal nerve, and here’s the superior gluteal nerve, disappearing beneath gluteus medius. The superior gluteal nerve supplies gluteus medius, gluteus minimus, and tensor fascia lata. The inferior gluteal nerve supplies gluteus maximus.

The sciatic nerve runs down the middle of the thigh. Deep to it are quadratus femoris, and lower down, adductor magnus. This is the long head of biceps femoris which crosses over the nerve obliquely, and covers it up. We’ll follow the sciatic nerve further, in the next section of this tape.

In the thigh, the sciatic nerve supplies semitendinosus, semimembranosus, and also biceps femoris, and the posterior part of adductor magnus.

Lastly, there are a few hip muscles which have their own individual nerve supply. Psoas major is supplied by several small branches of the lumbar plexus. Small separate branches of the sacral plexus supply piriformis, obturator internus, and quadratus femoris.