FASCI.^ 457 



(6) Posterior Group 

 (Figs. 387, 407, 408, 413) 



The muscles of this group arise from the ilium and sacrum, cover the dorso- 

 lateral surface of the hip, and are inserted into the great trochanter and shaft 

 of the femur and into the ilio-tibial band. They lie in three planes. In the first 

 layer (fig. 387) are the fiat, quadrilateral tensor fasciae latae, which arises from 

 the front of the crest of the ilium and is inserted into the ilio-tibial band, and the 

 thick, rhomboid gluteus maximus, which arises from the dorsal portion of the 

 iliac ala, the lumbo-dorsal fascia, the sacrum and coccyx, and the sacro-tuberous 

 (great sacro-sciatic) Hgament, and is inserted in part into the ilio-tibial band and 

 in part into the back of the upper part of the shaft of the femur. The ilio-tibial 

 band is a flat tendon which descends, closely fused with the fascia lata, to the 

 lateral side of the upper extremity of the tilDia. In the second layer (fig. 408) 

 are the flat, thick, triangular gluteus medius. and the 'pear-shaped' piriformis 

 The former arises from the upper and back part of the outer surface of the ala of 

 the ilium, the latter from the ventral surface of the sacrum and the posterior 

 border of the great sciatic notch. Both are inserted into the top of the great 

 trochanter. The third layer (fig. 409) is composed of the triangular gluteus 

 minimus, which arises from the inferior ventral portion of the outer surface of 

 the ala of the ilium, and is inserted into the front of the great trochanter of the 

 femur. 



The muscles of this group extend, flex, abduct, and rotate the thigh at the hip. 

 The gluteus maximus and medius are in part extensors, the gluteus minimus 

 and the tensor fasciae latae are flexors of the hip-joint. All the muscles serve to 

 abduct, the gluteus maximus acting thus when the hip is flexed. When the thigh 

 is extended the lower part of the gluteus maximus is an adductor. The gluteus 

 maximus and posterior part of the gluteus medius and the piriformis act as 

 lateral, the anterior part of the gluteus medius, the gluteus minimus, and the 

 tensor fasciae latae as medial, rotators. The gluteus maximus and the tensor 

 fasciae latae through the ilio-tibial band keep the extended knee-joint firm. 

 The gluteus maximus is supplied by the inferior gluteal nerve, the piriformis 

 by special nerves, and the other muscles of the group by the superior gluteal 

 nerve. All these nerves arise from the upper part of the back of the sacral 

 plexus. 



The gluteus medius, gluteus minimus, and piriformis form a group of muscles which in the 

 embryo have a common origin and are more or less fused in the adult. The gluteus maximus 

 arises in two distinct, though associated, portions, and the tensor fasciae latse as another dis- 

 tinct portion. The two muscles, however, are probably to be considered as parts of a primitive 

 caudo-pelvo-tibial musculature, while the gluteus medius group is represented in the lower forms 

 by an iUo-femoral musculature. The former group is often closely associated with the extensor 

 muscles of the thigh in the lower forms (frog), and in some of the lower mammals extends its 

 insertion to the plantar fascia (ornithorhynchus). In the arm this group is perhaps represented 

 by the deltoid, the latissimus dorsi, and the teres major, while the gluteus medius group is 

 represented by the subscapularis. 



FASCIA 



The tela subcutanea of the gluteal region is very thick, contains much fat, and is often 

 divisible into two layers, of which the deeper is closely adherent to the fascia lata and through 

 this to the gluteus maximus. Over the great trochanter a subcutaneous bursa is usually found 

 (bursa trochanterica subcutanea). 



Muscle fascia. — The muscles of the hip and thigh are enclosed in a dense fascia, the fascia 

 lata (figs. 387, 407). This arises from the tuber ischii, the sacro-tuberous (great sacro-sciatic) 

 hgament, the back of the sacrum and the coccyx, the crest of the ihum, the inguinal (Poupart's) 

 ligament, and the pubic and ischial rami, and extends to the tibia and the fascia covering the 

 muscles of the leg. It is composed mainly of bundles of fibres running transversely to the long 

 axis of the limb. In the region of the gluteal groove it is strengthened by a transverse fibrous 

 band which arises from the tuberosity of the ischium and arches upward over the lower border 

 of the gluteus maximus muscle. 



In the region of the hip the fascia lata invests both surfaces of the tensor fasciae latse and 

 the gluteus maximus, and is closely bound to these muscles through intramuscular septa. 

 Between these two muscles the fascia covers the fascia of the gluteus medius, to which it is 

 adherent near the ihac crest, but from which it is separated by loose tissue more distally. Anter- 

 iorly the fascia is fused with the ilio-pectineal fascia and the inguinal (Poupart's) ligament. 



