588 DISSECTION OF THE BUTTOCK. 



SCIATIC AND PUDIC VESSELS. The vessels on the back of the pelvis, 

 below the pyriformis muscle, are branches of the internal iliac (p. 513). 



The sciatic artery (fig. 200, b) 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 muscles, as far as the 

 lower border of the gluteus maximus : here 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 named branches : 



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

 great sacro-sciatic ligament and the gluteus 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. 



c. Muscular branches enter the gluteus maximus, the upper gemellus, 

 and obturator internus ; and by means of a branch to the quadratus, which 

 passes with the nerve of the same name beneath the gemelli and obturator 

 internus, it gives offsets to the hip joint and the inferior gemellus. 



d. Anastomotic branch (fig. 200, e). Varying in size this artery is 

 directed outwards to the root of the great trochanter, where it anastomoses 

 with the gluteal and internal circumflex. 



The pudic artery (fig. 200, d} belongs to the perinoeum and the genital 

 organs; it is smaller than the sciatic, internal to which it lies. Only the 

 small part of the vessel which winds over the ischial spine is seen on 

 the back of the pelvis, for it enters the perimeal space through the small 

 sacro-sciatic notch, and is there distributed (p. 390). 



It supplies a small branch over the back of the sacrum, which anasto- 

 moses with the gluteal and sciatic vessels ; and a twig from it accompanies 

 the nerve to the obturator internus muscle. 



The veins with the sciatic and pudic arteries receive contributing twigs 

 corresponding with the branches of those arteries at the back of the pelvis, 

 and open into the internal iliac vein. 



SCIATIC AND PODIC NERVES. The nerves appearing at the back of 

 the pelvis, below the pyriformis, are branches of the sacral plexus to the 

 lower limb (p. 518) ; they are furnished mostly to parts beyond the 

 gluteal region, but a few are distributed to the muscles at the back of 

 the pelvis. 



The small sciatic (fig. 200, 3 ) is a cutaneous nerve of the back of the, 

 thigh, for it supplies only one muscle of the buttock. It springs from the 

 lower part of the sacral plexus, generally by two pieces, and takes the 

 course of the sciatic artery as far as the lower border of the great gluteus, 

 where it gives many cutaneous branches : much diminished in size at that 

 spot, the nerve is continued along the back of the thigh beneath the fascia, 

 and ends below the knee in the integuments of the back of the leg. The 

 branches which are distributed to, or near the buttock, are muscular and 

 cutaneous : 



The muscular branches (inferior gluteal) enter the under surface of the 

 gluteus maximus near the lower border. 



The cutaneous branches are directed upwards and downwards at the 

 border of the gluteus : 



The ascending set (fig. 199) are distributed in the fat over the lower 

 third of the muscle. 



