338 MUSCLES AND FASCIAE. 



with the upper part of the tendon of the Obturator internus, and is inserted with 

 it into the upper border of the great trochanter. This muscle is sometimes 

 wanting. 



Relations. By its superficial surface, with the Gluteus maximus and the ischiatic 

 vessels and nerves. By its deep surface, with the capsule of the hip-joint. By its 

 upper border, with the lower margin of the Pyriformis. By its lower border, with 

 the tendon of the Obturator internus. 



The Gemellus Inferior arises from the upper part of the outer border of the 

 tuberosity of the ischium, and, passing horizontally outwards, is blended with the 

 lower part of the tendon of the Obturator internus, and inserted with it into the 

 upper border of the great trochanter. 



Relations. By its superficial surface, with the Gluteus maximus, and the 

 ischiatic vessels and nerves. By its deep surface, it covers the capsular ligament 

 of the hip-joint. By its upper border, with the tendon of the Obturator internus. 

 By its lower border, with the tendon of the Obturator externus and Quadratus 

 femoris. 



The Quadratus Femoris is a short, flat muscle, quadrilateral in shape (hence its 

 name), situated between the Gemellus inferior and the upper margin of the 

 .Adductor magnus. It arises from the outer border of the tuberosity of the 

 ischium, and, proceeding horizontally outwards, is inserted into the upper part of 

 the linea quadrati, on the posterior surface of the trochanter major. A synovial 

 bursa is often found between the under surface of this muscle and the lesser tro- 

 chanter, which it covers. 



Relations. By its posterior surface, with the Gluteus maximus and the sciatic 

 vessels and nerves. By its anterior surface, with the tendon of the Obturator 

 externus and trochanter minor. By its upper border, with the Gemellus inferior. 

 Its lower border is separated from the Adductor magnus by the terminal branches 

 of the internal circumflex vessels. 



Dissection. In order to expose the next muscle (the Obturator externus), it is necessary to 

 remove the Psoas, Iliacus, Pectineus, and Adductor brevis and Adductor longus muscles, from the 

 front and inner side of the thigh ; and the Gluteus maximus and Quadratus femoris, from the back 

 part. Its dissection should consequently be postponed until the muscles of the anterior and 

 internal femoral regions have been examined. 



The Obturator Externus is a flat triangular muscle, which covers the outer sur- 

 face of the anterior wall of the pelvis. It arises from the margin of bone imme- 

 diately around the inner side of the obturator foramen, viz., from the body and 

 ramus of the pubes, and the ramus of the ischium ; it also arises from the inner 

 two-thirds of the outer surface of the obturator membrane, and from the tendinous 

 arch which completes the canal for the passage of the obturator vessels and nerves. 

 The fibres converging pass outwards and backwards, and terminate in a tendon 

 which runs across the back part of the hip-joint, and is inserted into the digital fossa 

 of the femur. 



Relations. By its anterior surface, with the Psoas, Iliacus, Pectineus, Adductor 

 longus, Adductor brevis, and Gracilis ; and more externally, with the neck of the 

 femur and capsule of the hip-joint. By its posterior surface, with the obturator 

 membrane and Quadratus femoris. 



Nerves. The Gluteus maximus is supplied by the inferior gluteal nerve and a 

 branch from the sacral plexus. The Gluteus medius and Gluteus minimus, by the 

 superior gluteal. The Pyriformis, Gemelli, Obturator internus, and Quadratus 

 femoris, by branches from the sacral plexus ; and the Obturator externus, by the 

 obturator nerve. 



Actions. The Glutei muscles, Avhen they take their fixed point from the pelvis, 

 are all abductors of the thigh. The Gluteus maximus and the posterior fibres of 

 the Gluteus medius rotate the thigh outwards ; the anterior fibres of the Gluteus 

 medius and the Gluteus minimus rotate it inwards. The Gluteus maxirnus serves 

 to extend the femur, and the Gluteus medius and Gluteus minimus draw it forwards. 

 The Gluteus maximus is also a tensor of the fascia lata. Taking their fixed point 



