430 THE MUSCLES AND FASCIA. 



The G-emelli are two small muscular fasciculi, accessories to the tendon of the 

 Obturator internus, which is received into a groove between them. They are called 

 superior and inferior. 



The Gemellus superior, the smaller of the two, arises from the outer surface 

 of the spine of the ischium, and, passing horizontally outward, becomes blended 

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

 it into the inner surface of the great trochanter. This muscle is sometimes 

 wanting. 



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

 sciatic 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 tuberosity of the 

 ischium, where it forms the lower edge of the groove for the Obturator internus 

 tendon, and, passing horizontally outward, is blended with the lower part of the 

 tendon of the Obturator internus, and is inserted with it into the inner surface of 

 the great trochanter. 



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

 sciatic vessels and nerves ; by its deep surface, with 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 upper part of the external lip of the tuber- 

 osity of the ischium, and, proceeding horizontally outward, is inserted into the 

 upper part of the linea quadrata ; that is, the line which crosses the posterior inter- 

 trochanteric line. A synovial bursa is often found between the under surface of 

 this muscle and the lesser trochanter, 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 and with the capsule of the hip-joint ; 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 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 explained. 



The Obturator externus (Fig. 257) is a flat, triangular muscle, which covers the 

 outer surface of the anterior wall of the pelvis. It arises from the margin of 

 bone immediately around the inner side of the obturator foramen, viz., from the 

 body and ramus of the os pubis 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 obtu- 

 rator vessels and nerves. The fibres from the pubic arch extend on to the 

 inner surface of the bone, from which they obtain a narrow origin between the 

 margin of the foramen and the attachment of the membrane. The fibres con- 

 verging pass backward, outward, and upward, 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 

 magnus, and Adductor brevis ; and more externally, with the neck of the femur 

 and capsule of the hip-joint. The obturator artery and vein lie between this 

 muscle and the obturator membrane ; the superficial part of the obturator nerve 

 lies above the muscle, and the deep branch perforates it; by ite posterior surface, 

 with the obturator membrane and Quadratus femoris. 



Nerves. The Gluteus maximus is supplied by the fifth lumbar and first and 



