354 THE MUSCLES 



crest of the ilium to the greater troeliantur. This is ])y far the most imi)ortant and 

 frecjuent of its actions. In walkinu", if it were not for the powerful contraction of 

 the gluteus medius and its associated muscles the gluteus minimus and the tensor 

 vaginie femoris, the pelvis Avould not l:)e held firm upon the upper part of the thigh 

 when one leg is upon the ground and the other is being advanced in the forward 

 step. In fast Avalking the rotatory action of the muscle comes into play, for not 

 only does the gluteus medius of the limb Avhich is resting upon the ground supi)ort 

 the pelvis by drawing downwards the crest of the ilium, l:)ut, l;)y drawing back- 

 wards the front portion of that crest, it throws forwards the opposite side of the 

 pelvis and increases the length of the stride. 



Relations. — Superficially, the fascia lata, gluteus maximus, and tensor vaginae 

 femoris; deeply, the gluteus minimus, sujierior gluteal vessels and nerve, and the 

 greater trochanter. 



Variations. — Sometimes a partially distinct bundle of fibres is inserted into the front of the 

 upper border of the greater trochanter. A slip may be giveu from the lower border to the 

 pyriformis. 



Third Layer 



The third layer consists of one muscle — the gluteus minimus — which is con- 

 tinuous Avith the external rotators which form the next group. 



GLUTEUS MINIMUS 



The gluteus minimus (fig. 290) — named from its position and smaller size — is 

 a thick triangular sheet. 



Origin. — (1) The outer surface of the ilium between the middle and inferior 

 gluteal lines; (2) a fibrous septum which intervenes between its fibres and those of 

 the gluteus medius below the anterior superior spine; (3) the front of the capsule 

 of the hi]3- joint. 



Insertion. — The well-marked vertical impression which forms the anterior 

 border of the greater trochanter. 



Structure. — From the fleshy origin the fibres converge fanwise upon the deep 

 surface of the tendon which is first seen about the middle of the anterior border, 

 and then covers the lower part of the muscle. By its anterior border this muscle 

 is closely blended with the anterior border of the gluteus medius and with some of 

 the ligaments of the hip-Joint. Like the preceding muscle, it is also much thicker 

 and stronger in front. 



Nerve-supply. — From the same sources as the preceding by the superior 

 gluteal nerve which distributes filaments to the middle of its outer surface near 

 its posterior border. 



Action. — The same as the preceding: viz. to abduct and rotate inwards the hip- 

 joint; and when it takes its fixed point from below, as is most usually the case, to 

 flex the pelvis laterally and at the same time to rotate the other side forwards. 



Relations. — Sui)erficially, the gluteus medius, the superior gluteal vessels and 

 nerve; deeply, the capsule of the hip- joint, and posterior head of the rectus 

 femoris. 



Variations. — The front part of the musele may be separate from the rest. It occasioually 

 sends slips to the adjacent muscles. 



THE EXTERNAL ROTATORS OF THE THIGH 



This group consists of six somewhat short muscles, wliich run transversely from 

 the pelvic l)ones to the femur, and which follow innnediately after the lower fibres 

 of the gluteus mininnis — viz. the pyriformis, the obturator "internus with the two 

 gemelli, the quadratus feiuoris, and the obturator cxteruus. 



