352 THE MUSCLES 



tendinous fibres, wliicli are not only attached to tlie roujrh process of tlie l)one but 

 to the adjacent tendon of the vastus externus, while the more su])erticial fibres still 

 pass on to be attached to the fascia lata. The whole muscle forms a parallelogram 

 of which the upper and lower parallel sides are formed by the origin and insertion 

 which run in oljlique lines downwards and iuAvards, w^hile the outer and inner 

 borders of the muscle running downwards and outwards form the other two sides 

 of the parallelogram. This nmscle is especially remarkable for the large size of the 

 fasciculi in which its fleshy fibres are arranged, and which give the muscle its 

 peculiarly coarse appearance. 



There are two well-marked bursffi in connection with the deep surface of this 

 muscle: the one over the tul)erosity of the ischium, which is jjartly covered by 

 the muscle and partly projects from the middle of its knver l)order in such away that 

 Avhen the thigh is extencled it intervenes between the muscle and the prominence 

 of bone, and when the thigh is flexed it lies between the tuberosity of the ischium 

 and the subcutaneous fat. The second is a large, often multilocular cavity which 

 se]:)arates the outer surface of the greater trochanter from the aponeurosis of insertion 

 of the upper part of the muscle. A small bursa is also occasionally found between 

 the lower part of the muscle and the tendon of the vastus externus. 



Nerve-supply. — From the sacral plexus (through the fifth lumbar and the first 

 and second sacral nerves), by means of the inferior gluteal branches which enter 

 the deep surface of the muscle close to its inferior and internal border. 



Action. — To extend the hip-joint. The upper part of the muscle, passing over 

 the greater trochanter, is placed at a consideral)le distance from the axis of movement 

 which passes through the centre of the hip-joint. A similar object is obtained by 

 the insertion of the lower fibres of the muscle at some distance down the back of 

 the femur. The whole muscle therefore is able to act as an extensor of the hip- 

 joint with much less mechanical disadvantage than is usual in the body. The 

 gluteus maximus is not used in the movements of extension which recjuire but 

 little muscular power, such as those which draw the thigh backwards in walking; 

 for this purpose the contraction of the hamstring muscles at the back of the thigh 

 is alone employed. AVhere, however, a greater effort is required, as in ascending 

 a hill or in running and leaping, the gluteus maximus acts with great power. 



It has some influence as an external rotator. With respect to abduction and 

 adduction, the action of the muscle is neutral. Acting alone, its upper fibres will 

 assist in the former, and its lower fibres in the latter movement. By means of the 

 ilio-tibial band it makes tense the outer portion of the fascia lata and is able to 

 exert some force in the extension of the knee, especially Avhen that movement is 

 nearly completed. Taking its fixed point from below, the gluteus maximus is a 

 powerful extensor of the pelvis and in some degree of the lower part of the s}>ine, 

 e.g. in rising from the stooping position or Avhere the trunk in a sitting posture is 

 drawn forcibly l>ackwards as in the action of rowing. The influence Avhich it has 

 upon the back by means of its attachment to the lumbar aponeurosis is shown by 

 the great pain which is felt in rising from the stooping position when there is any 

 inflammation of the fascise in this region, as in lumbago. 



Relations. — Behind, the thick adipose tissue of the buttock and numerous 

 cutaneous ncrA'os; in front, the gluteus medius, pyriformis, gemelli and obturator 

 internus, ([uadratus femoris, adductor magnus, biceps, semi-tendinosus and semi- 

 menibranosus, the gluteal, sciatic and pudic vessels, the great and small sciatic, the 

 pudic and internal ol)turator nerves, the two sacro-sciatic ligaments, the tuber 

 isehii, and greater trochanter. 



Variations. — These are rare. Occasionally a bilaruinar arrangement has been observed. 



2. TENSOR VAGINA. FEMORIS 



The tensor vaginae femoris Cfigs. 2S7 and 803) — named from its function of 

 making tight the fascia lata, or sheath of tlie thigh (= vagina femoris) is an 

 elongated, four-sided sheet. 



Origin. — (1) Tim front of the outer lip of the crest of the ilium; (2) the upi)er 



