172 THE NERVOUS SYSTEM 



rectum a routine measure in the initial stages of treatment of 

 all cases of sciatica. 



Owing to its position, the plexus may be injured during 

 parturition in difficult labours. 



The Superior Gluteal Nerve (L. 4 and 5, and S. i) arises 

 from the posterior aspect of the plexus and enters the gluteal 

 region by passing through the great sciatic foramen. It gives 

 off no cutaneous branches, but it supplies the glutaei, medius 

 and minimus, and the tensor fasciae latae. 



The Glutaus Medius arises from the dorsum ilii and its fibres converge 

 on the lateral aspect of the greater trochanter of the femur, passing above 

 the capsule of the hip-joint, from which they are separated by the glutseus 

 minimus. The medius acts as a powerful abductor of the thigh ; in 

 addition, the anterior fibres act as flexors and medial rotators, while the 

 posterior fibres act as lateral rotators of the hip. The upper and anterior 

 part of the muscle is covered by the skin and fasciae, but the greater bulk 

 of the muscle is hidden from view by the glutceus maximus. 



The Glutceus Minimus lies under cover of the preceding muscle and is 

 therefore deeply placed. From their origin on the lower part of the 

 dorsum of the ilium, the fibres converge on the anterior aspect of the 

 greater trochanter where they receive insertion. The action, like the 

 nerve-supply, of this muscle is the same as that of the glutreus medius. 



The Tensor Fascia Latiz arises from the anterior part of the lateral lip 

 of the iliac crest and is inserted into a splitting of the deep fascia on the 

 lateral aspect of the thigh. Through the ilio-tibial tract (band) of the deep 

 fascia, the muscle exercises an extensor action on the knee-joint, and by 

 bracing the tract it helps to relieve the strain from the quadriceps when 

 the erect attitude is maintained. Further, the tensor fascioe latse acts as 

 a weak abductor and medial rotator of the hip-joint. 



The Ilio-tibial Tract (Band) is the thickened lateral part of the deep 

 fascia of the thigh. Distally, it blends with the periosteum over the 

 lateral condyle of the tibia and the head of the fibula and proximally it is 

 attached to the lateral lip of the iliac crest. It forms such a strong sheet 

 that extravasations of blood on its deep surface do not rupture through it, 

 but extend distally or forwards before discoloration becomes visible. 



The Inferior Gluteal Nerve (L. 5 and S. i and 2) also arises 

 from the posterior aspect of the plexus and passes through the 

 greater sciatic foramen to enter the buttock, where it is 

 entirely distributed to the glutceus maximus. The latter muscle 



