Gray's Fig. 829 - Dissection of side wall of pelvis showing sacral and pudendal plexuses.
In human anatomy, the Sacral plexus refers to the nerveplexus emerging from the sacralvertebrae (S1-S4), and which provides nerves for the pelvis and lower limbs.
The phrase "Lumbar sacral plexus" is also sometimes used, and in this context it refers to the nerves emerging from L4-S4.
The sacral plexus is formed by the lumbosacral trunk, the anterior division of the first, and portions of the anterior divisions of the second and third sacral nerves.
The lumbosacral trunk comprises the whole of the anterior division of the fifth and a part of that of the fourth lumbar nerve; it appears at the medial margin of the Psoas major and runs downward over the pelvic brim to join the first sacral nerve. The anterior division of the third sacral nerve divides into an upper and a lower branch, the former entering the sacral and the latter the pudendal plexus.
The nerves forming the sacral plexus converge toward the lower part of the greater sciatic foramen, and unite to form a flattened band, from the anterior and posterior surfaces of which several branches arise. The band itself is continued as the sciatic nerve. which splits on the back of the thigh into the tibial and common peroneal nerves; these two nerves sometimes arise separately from the plexus, and in all cases their independence can be shown by dissection.
Relation
The sacral plexus lies on the back of the pelvis between the Piriformis and the pelvic fascia (Fig. 829); in front of it are the hypogastric vessels, the ureter and the sigmoid colon. The superior gluteal vessels run between the lumbosacral trunk and the first sacral nerve, and the inferior gluteal vessels between the second and third sacral nerves.
All the nerves entering the plexus, with the exception of the third sacral, split into ventral and dorsal divisions, and the nerves arising from these are as follows:
The Nerve to the Quadratus femoris and Gemellus inferior arises from the ventral divisions of the fourth and fifth lumbar and first sacral nerves: it leaves the pelvis through the greater sciatic foramen, below the Piriformis, and runs down in front of the sciatic nerve, the Gemelli, and the tendon of the Obturator internus, and enters the anterior surfaces of the muscles; it gives an articular branch to the hip-joint.
The Nerve to the Obturator internus and Gemellus superior arises from the ventral divisions of the fifth lumbar and first and second sacral nerves. It leaves the pelvis through the greater sciatic foramen below the Piriformis, and gives off the branch to the Gemellus superior, which enters the upper part of the posterior surface of the muscle. It then crosses the ischial spine, reënters the pelvis through the lesser sciatic foramen, and pierces the pelvic surface of the Obturator internus.
The Nerve to the Piriformis arises from the dorsal division of the second sacral nerve, or the dorsal divisions of the first and second sacral nerves, and enters the anterior surface of the muscle; this nerve may be double.
