GLUTEUS MEDIUS 353 



part of the notch between the anterior sujierior and the anterior inferior spines of 

 the ilium; (o) the inner surface of the fascia lata, l)y which it is closely invested. 



Insertion. — The fascia lata ahout one-fourth of the way down the outer side of 

 the thigh. 



Structure. — The muscle consists of ])arallel Heshy fibres which arise by a 

 short tendinous sheet, pass obliquely downwards, outwards, and backwards, and 

 are inserted between two layers of the upper part of the strong aponeurosis of the 

 fascia lata on the outside of the thigh called the ilio-tihial band, which also gives 

 attachment to the majority of the fibres of the gluteus maximus. The two muscles 

 meet by their adjacent Ijorders a little below the upper part of the greater trochanter 

 at an angle of about 60°. As they pass upwards, the two divisions of the fascia 

 lata form a strong sheath for the muscle. 



Nerve-supply. — Through the fourth and fifth lumbar nerves, and the first 

 sacral, Ijy the terminal branch of the superior gluteal nerve which enters the muscle 

 about the middle of its deep surface near its posterior border. 



Action. — To abduct and rotate inwards the thigh, and, taking its fixed point 

 from below, to support the pelvis and to rotate the other side of it forwards. 

 Acting with the gluteus maximus, it will draw upwards the ilio-tibial band, the 

 obliquity of its fibres enabling it to counteract the tendency of that muscle to draw 

 the l)and backwards. The chief consequence of this traction upon the ilio-tibial 

 Itand will be to assist in the latter part of the extension of the leg, by the drawing 

 upwards of the external tuberosity of the tibia. 



Relations. — Superficially, the fascia lata and the origin of the sartorius; 

 deeply, the deeper layer of the fascia lata, the gluteus medius, the upper part of 

 the rectus femoris and the vastus externus, with some of the branches of the 

 external circumflex artery. 



Second Layer 



The second layer consists of one muscle — 



GLUTEUS MEDIUS 



The gluteus medius (fig. 288) — named from its size and position, which are 

 intermediate between those of the great and small gluteal muscles — is a strong 

 triangular sheet. 



Origin. — (1) The anterior four-fifths of the outer lip of the crest of the ilium; 

 (2) the outer surface of the ilium, bordered al)Ove by the middle portion of the 

 outer lip of the crest of the ilium, and in the posterior fifth by the superior gluteal 

 line, below by the middle gluteal line; (3) the strong process of the fascia lata 

 which invests the outer surface of the muscle and separates it behind from the 

 gluteus maximus; (4) the intermuscular septum which intervenes between it and 

 the gluteus minimus just Ijelow the anterior superior spine of the ilium. 



Insertion. — The well-marked oblic{ue impression extending from the posterior 

 superior to the anterior inferior angle on the outer surface of the greater trochanter. 



Structure. — Arising by fleshy and tendinous fibres intermingled, the muscle 

 converges fanwise ujion V)oth surfaces of a strong flat tendon which is visible rather 

 higher ui)on the deep than the outer surface of the muscle. The front part of the 

 nuiscle is stronger, and it gradually decreases in thickness towards its posterior 

 edge. A Inirsa is contained l)etween the deeji i»ortion of the tendon and the 

 triangular space that lies in front of the impression upon the outer surface of tlie 

 greater trochanter. 



Nerve-supply. — From the fourth and fifth lumbar nerves, and the first sacral 

 nerve by branches of the superior gluteal nerve which enter the deep surface of the 

 muscle near the middle of its ])osterior border. 



Action. — To abduct the hip-joint. It will also by its thicker and stronger 



anterior fibres rotate the thigh inwards. Its posterior fil)res, on the other hand, 



which are not so strong will tend slightly to rotate the thigh outwards. Acting 



from below, it tends to support the pelvis upon the fenuu* and to approximate the 



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