DISSECTION OF THE POSTERIOR LIMB. 67 



convexity of the same trochanter by means of a synovial bursa, and 

 becomes inserted into the crest. 3. By a triangular iieshy slip, into the 

 back of the trochanteric ridge. 



Action. — To extend and abduct the hip. In the former of these 

 actions, when the limb is free to move, the femur, and with it the 

 whole limb, is carried backwards ; but when the femur is fixed it raises 

 the trunk, as in rearing. 



Directions. — The last-described muscle must be removed in order to 

 expose the deep gluteus and the other structures which it covers. A 

 deep incision should be made through the muscle along the crest of the 

 ilium, and the muscle is to be turned down by severing its fibres at 

 their origin. Care must be taken, in doing this, to avoid cutting the 

 subjacent deep gluteus, whose fibres may be recognised, as soon as they 

 are reached, by their insertion within the great trochanter. A reference to 

 Plate 16 may here be useful. The semitendinosus is to be turned down in 

 the same manner, by severing its superior attachments ; and this muscle 

 and the biceps may be removed to the extent shown in the Plate. In 

 performing this dissection the gluteal nerves and vessels and the ischiatic 

 vessels are unavoidably severed, but a look-out should be kept for these, 

 and they should be cut about the points shown in the figure. 



The Gluteal Abtbey (Plate 16) is a branch given off from the 

 internal iliac within the pelvis. After a very short course it splits into 

 several branches, which, emerging by the great sacro-sciatic opening, 

 are distributed to the gluteal muscles. 



The Ischiatic Aktety (Plate 16) is one of the terminal branches 

 of the lateral sacral artery, which, again, is a collateral branch of the 

 internal iliac. It perforates the sacro-sciatic ligament near the edge of 

 the sacrum, and is distributed in the biceps and semitendinosus. 



Veins of the same names accompany the foregoing arteries. 



The Internal Pudic Artery. The dissection of this artery belongs to 

 another region, but the vessel is generally visible here in a part of its course. 

 A few inches of it are represented in Plate 16, as showing faintly through 

 the texture of the sacro-sciatic ligament. It is described at page 354. 



The Glutea'l Nerves (Plate 16). These nerves, which are derived 

 from the lumbo-sacral plexus, issue from the great sacro-sciatic opening 

 in company with the gluteal vessels and the great sciatic nerve. They 

 consist of an anterior and a posterior set. 



The Anterior gluteal nerves are three or four in number. One of 

 them passes downwards and forwards between the middle and internal 

 gluteal muscles, to reach the tensor vaginae femoris and anterior division 

 of the superficial gluteus. Another branch passes downwards over the 

 deep gluteus, to which it is distributed. One or two other branches 

 supply the middle gluteus. 



The Posterior gluteal nerves are two in number — an upper and a 



