590 DISSECTION OF THE BUTTOCK. 



and its insertion is the same as that of the obturator tendon. This mus- 

 cle is placed between the obturator internus and quadratus, but near the 

 femur the tendon of the obturator externus comes into contact with its 

 lower border. 



Action. These small fleshy slips seem to be but accessory pieces of 

 origin to the internal obturator, with which they combine in use. 



The OBTURATOR INTERNUS (fig. 200, D ) arises from the innominate 

 bone inside the pelvis (p. 543), and passes to the exterior through the 

 small sacro-sciatic notch. The tendon of the muscle is directed outwards 

 over the hip-joint, and is inserted with the gemelli into the upper part of 

 the great trochanter, in front of the pyriformis, as well as into the con- 

 tiguous portion of the neck of the femur. 



Outside the pelvis the obturator is mostly tendinous, and is embraced 

 by the gemelli muscles in the following way: near the pelvis the gemelli 

 meet beneath, but near the trochanter they cover the tendon. Beneath 

 the obturator is a synovial sac. Crossing the muscle are the large and 

 small sciatic nerves and the sciatic vessels; and covering the whole is the 

 glutens maximus. On cutting through the tendon and raising the inner 

 end, it will be found divided into three or four pieces as it turns over the 

 margin of the pelvis (fig. 201, H ) ; at this spot the pelvis is marked by 

 ridges of fibro-cartilace, which correspond with the intervals between the 

 tendons, and the surfaces are lubricated by a synovial membrane. 



Action. Acting from the hinder border of the pelvis round which 'it 

 turns, it rotates out or abducts the femur according as this bone tnay be 

 hanging or raised. It will erect the pelvis after stooping, and will balance 

 the same in standing; and it will rotate to the opposite side the trunk 

 supported on one limb. 



The QUADRATUS FEMORis (fig. 200, G ) has the form expressed by its 

 name, and is situate between the inferior gemellus and the adductor mag- 

 nus. Internally it arises from the outer border of the tuber ischii for 

 two inches, along the origin of the semi-membranosus and adductor mag- 

 nus ; externally it is inserted into a tubercle in the posterior intertrochan- 

 teric ridge, and slightly into the neck of the femur ; and into a line on 

 the upper end of the bone for about two inches above the attachment of 

 the great adductor. 



By one surface it is in contact with the sciatic vessels and nerves, and 

 the gluteus. By the other it rests on the obturator externus, the internal 

 circumflex vessels, and its small nerve and vessels. Between its lower 

 border and the adductor magnus one of the terminal branches of the inter- 

 nal circumflex artery issues. Between it and the small trochanter is a 

 bursa, which is common also to the upper part of the adductor magnus. 



Action. Though the muscle has but slight power, it will be associated 

 with the other muscles on the back of the pelvis in rotation out of the 

 pendent femur, and in abduction of the femur when the hip-joint is bent. 



And its femoral attachment being fixed, it will help in supporting the 

 pelvis; or it will turn the face to the opposite side, the body being sup- 

 ported on one limb. 



Dissection (fig. 201). The quadratus and the gernelli muscles may be 

 now cut across, in order that their small nerve and artery, the ending of 

 the internal circumflex artery, and the obturator externus may be dis- 

 sected out. 



The internal circumflex branch (fig. 201, /) of the profunda artery (p. 

 578) divides finally into two parts. One (</) ascends beneath the quad- 



