. NERVES OF DISTRIBUTION FROM THE SACRAL PLEXUS. 607 
The nerve to the quadratus femoris (and inferior gemellus) arises from the 
front of the fourth and fifth lumbar and first sacral nerves. It passes down- 
wards over the back of the capsule of the hip-joint (to which it sends a fine 
branch) beneath the sacral plexus, gemelli, and obturator internus muscles. It 
supphes a nerve to the inferior gemellus, and terminates in the deep surface of the 
quadratus femoris. 
The nerve to the obturator internus (and superior gemellus) arises from the 
anterior aspect of the fifth lumbar and first two sacral nerves. In the buttock it 
lies below the great sciatic nerve on the outer side of the pudic vessels; crossing 
the ischial spine, it enters the ischio-rectal fossa through the lesser sciatic foramen. 
The nerve supphes in the buttock a branch to the superior gemellus, and terminates 
by entering the pelvic surface of the obturator internus. 
The nerve to the hamstring muscles forms the innermost part of the great 
sciatic trunk in the lower part of the buttock. It arises from all the roots of the 
tibial nerve on their anterior aspect, viz., from the fourth and fifth lumbar and 
the first three sacral nerves. These roots unite to form a cord which is closely 
associated with the tibial nerve and is placed in front of and afterwards on its 
inner side. Extending into the thigh, the trunk is distributed to the hamstring 
muscles by means of two sets of branches. Just below the level of the ischial 
tuberosity an upper set of nerves passes inwards to enter the upper part of the 
semitendinosus and the ischial head of the biceps. Lower down in the thigh the 
remaining portion of the nerve separates off from the great sciatic (tibial) trunk 
and supplies branches to the semimembranosus, the lower part of the semitendi- 
nosus, and the adductor magnus. 
Articular branches for the hip-joint arise from the nerve to the quadratus 
femoris, and often directly from the front of the great sciatic (tibial) nerve near 
its origin. They enter the back of the capsule of the joint in the region of the 
buttock. 
The posterior branches are: (a) muscular branches, viz. a nerve to the 
pyriformis, the superior gluteal nerve, the inferior gluteal nerve, and a nerve to the 
short head of the biceps ; (@) articular branches (to the knee-joint). 
These nerves all arise from the back of the roots of the sacral plexus, associated 
with the origin of the peroneal nerve. 
The nerve to the pyriformis muscle may be double. It arises from the back 
of the second, or first and second sacral nerves, and at once enters the anterior 
surface of the muscle. 
The superior gluteal nerve (n. glutzeus superior) arises from the back of the 
fourth and fifth lumbar and first sacral nerves, and is directed backwards and 
outwards into the buttock, above the pyriformis muscle, along with the gluteal 
artery. Under cover of the gluteus maximus and gluteus medius, it extends 
outwards over the gluteus minimus, along with the inferior part of the deep gluteal 
artery, to the under surface of the tensor vagine femoris, in which it ends. On 
its way it supplies branches to the gluteus medius and gluteus minimus. 
The inferior gluteal nerve (n. glutzeus inferior) arises from the back of the fifth 
lumbar and first two sacral nerves. It appears in the buttock at the lower border of 
the pyriformis muscle, superficial to the great sciatic nerve, and at once breaks up 
into anumber of branches for the supply of the gluteus maximus. In its course in 
the buttock it is closely associated with the small sciatic nerve. Its origin is 
sometimes combined with that of the following nerve. 
The nerve to the short head of the biceps springs from the outer side of the 
great sciatic (peroneal) trunk in the upper part of the thigh. When traced to its 
origin, it is found to arise (sometimes in combination with the inferior gluteal nerve) 
from the fifth lumbar and first two sacral nerves. In its course it is closely 
applied to the outer side of the peroneal nerve, from which it separates in the 
middle third of the thigh, usually in combination with the articular branches of 
that nerve for the knee-joint. In some cases it has an independent course in the 
thigh, and it may be associated in the buttock with the inferior gluteal nerve. 
An articular branch for the outer side and front of the knee-joint generally 
arises from the great sciatic or peroneal nerve in common with the nerve to the 
