118 



DISSECTION OF THE BUTTOCK. 



insertion 



relations in 

 foramen, 



in buttock ; 



use with 

 femur hang- 

 ing, and 

 raised ; 



both limbs 

 on ground, 



only one. 



Dissect out 

 the chief 

 vessels and 

 nerves, 



and mus- 

 cular ) 

 branches. 



The vessels 

 come from 

 the iliac. 



Sciatic 

 artery : 



course 

 and ending 



branches ; 

 coccygeal ; 



branch to 

 sciatic 

 nerve ; 



from the front of the sacrum between and outside the second, 

 third, and fourth foramina, and leaves that cavity through the 

 great sacro-sciatic foramen to end in a rounded tendon, which is 

 inserted into the upper edge of the great trochanter of the femur 

 (fig. 60, p. 157). 



The muscle occupies the greater part of the sacro-sciatic foramen, 

 and divides the vessels and nerves passing through that aperture 

 into two groups : Above it are the gluteal vessels and the superior 

 glu teal nerve ; and below it the sciatic and pudic vessels and nerves, 

 and some other branches of the sacral plexus. Its upper border is 

 contiguous to the glutens medius ; and its lower, to the superior 

 gemellus. Like the other rotator muscles in this situation, it is 

 covered by the glutens maximus, and by the glutens medius at the 

 insertion ; it rests on the glutens minimus, which separates it from 

 the hip-joint. Its tendon is united by fibrous tissue to that of the 

 obturator and gemelli. 



Action. The pyriformis rotates out the femur when that bone is in 

 a line with the trunk ; but if the hip-joint is bent it abducts the limb. 



Both limbs being fixed, the muscles balance the pelvis, and help 

 to make the trunk erect after stooping to the ground. In standing 

 on one leg, besides assisting to support the trunk, the pyriformis 

 turns the face to the opposite side. 



Dissection, The pyriformis may now be cut across and raised 

 towards the sacrum, to allow the dissector to follow upwards the 

 sciatic and pudic vessels, and to trace the accompanying nerves to 

 their origin from the sacral plexus. 



A small nerve to the obturator interims (fig. 50, 5 ) and gemellus 

 superior is to be sought for in the fat at the lower border of the 

 plexus passing over the spine of the ischium on the outer side of the 

 internal pudic artery. A branch to the quadratus and inferior 

 gemellus ( 6 ) may be found by raising the trunk of the great sciatic 

 nerve ; but this w r ill be followed to its termination after the muscles 

 it supplies have been seen. 



SCIATIC AND PUDIC VESSELS. The arteries on the back of the 

 pelvis, below the pyriformis muscle, are branches of the internal 

 iliac, which will be described in dissection of the pelvis. 



The SCIATIC ARTERY (fig. 48) supplies the buttock below the 

 gluteal. After escaping from the pelvis below the pyriformis, 

 it descends with the small sciatic nerve over the gemelli and 

 obturator interims muscles, as far as the lower border of the glutens 

 maximus ; in its course the artery gives off many branches with the 

 superficial offsets of its companion nerve ; and, much reduced in 

 size, it is continued with that nerve along the back of the thigh. 

 In this course it furnishes the following branches : 



a. The coccygeal branch arises close to the pelvis, perforates the 

 great sacro-sciatic ligament and the glutens maximus, and ramifies 

 in this muscle, and on the back of the sacrum and coccyx. 



b. The branch to the great sciatic nerve (comes nervi ischiadici) is 

 very slender, and entering the nerve near the pelvis, ramifies in it 

 along the thigh. 



