THE INTERNAL ILIAC ARTERY. 815 



of the sciatic notch is felt for with the finger through the interspace between the pyri- 

 formis and the gluteus medius. The artery may be found as it turns over the bony 

 tip of the sacro-sciatic foramen towards the dorsum ilii. The sciatic artery may be 

 reached through the same incision, the finger then being carried below the pyriformis 

 muscle, when the spine of the ischium and the sharp edge of the sacro-sciatic ligament 

 will serve as landmarks. 



The point of emergence of both the sciatic and internal pudic arteries is indicated 

 with sufficient accuracy by the junction of the lower and middle thirds of a line drawn 

 from the tuberosity of the ischium to the posterior superior spine of the ilium. The 

 incision employed should follow the direction of the fibres of the greater gluteal 

 muscle. 



10. The Sciatic Artery. — The sciatic artery (a. glutaea inferior) (Fig. 727) is 

 one of the two terminal branches of the anterior division of the internal iliac. It lies 

 at first internal and posterior to the internal pudic artery, and is directed downward 

 and backward towards the lower part of the great sacro-sciatic foramen, passing usu- 

 ally below the fourth sacral nerve. It makes its exit from the pelvis through the great 

 sacro-sciatic foramen, below the pyriformis muscle, and bends downward beneath 

 the gluteus ma.ximus. It crosses the internal pudic artery at about the level of the 

 spine of the ischium, and in the rest of its course lies to the inner side of the great 

 sciatic nerve. It descends upon the gemelli, the internal obturator, and the quad- 

 ratus femoris, and, after giving off its principal branches, is continued down the leg 

 as a slender vessel, the comes nervi ischiadici. 



Branches. — Withi?t the pelvis the sciatic artery gives off some small and inconstant branches 

 to the internal obturator and pyriformis muscles and to the trunks of the sacral pelvis. 

 Outside the pelvis it gives rise to several larger branches. 



(a) The coccygeal branch passes inward and pierces the great sacro-sciatic ligament and 

 the gluteus maximus near its origin, terminating in the tissues over the lower part of the sacrum 

 and coccyx. 



[b) Muscular branches, variable in number, pass to the neighboring muscles, some of 

 them being continued beneath the quadratus femoris to reach the capsule of the hip-joint. 

 One branch somewhat larger than the rest can frequently be seen entering the deep surface of 

 the gluteus maximus in company with the inferior gluteal nerve ; it supplies the muscle and 

 forms anastomoses with the gluteal artery. 



{c) An anastomotic branch passes transversely outward, usually beneath the great sciatic 

 nerve, towards the greater trochanter of the femur. It gives twigs to the gemelli muscles, and 

 in the neighborhood of the trochanter anastomoses with the terminal branch of the internal cir- 

 cumflex, with the transverse branch of the external circumflex, and, below, with the first per- 

 forating artery, completing what is termed the crucial anastomosis. 



{d ) Cutaneous branches, variable in number, wind around the lower border of the gluteus 

 maximus in company with branches of the small sciatic nerve, and supply the integument over 

 the lower part of the gluteal region. 



(<?) The a. comes nervi ischiadici is the continuation of the sciatic artery. It is a long, 

 slender branch which passes downward upon or in the substance of the great sciatic ner\e, sup- 

 plying it and anastomosing with the perforating branches of the profunda femoris. 



Variations. — The occasional origin of the sciatic from the gluteal artery or from the 

 hypogastric axis has already been described in connection with the variations of the internal 

 iliac (page 808). Occasionally it has a double origin from both the gluteal and the anterior 

 division of the internal iliac, or it may be double, owing to the existence of stems, from each of 

 these vessels which pursue independent courses. 



In addition to its normal branches, it may give origin to the lateral sacral, the inferior 

 vesical, and the uterine or the middle hemorrhoidal. Especial interest attaches to the comes 

 nervi ischiadici, which occasionally traverses the entire length of the thigh to unite below with 

 the popliteal artery. It represents the original main stem of the sciatic artery, of which the 

 popliteal was primarily the continuation, the connection of that artery with the femoral, and the 

 subsequent diminution of the sciatic being secondary arrangements (page 824). 



11. The Internal Pudic Artery. — The internal pudic artery (a. pudenda 

 interna) (Fig. 727) is the other terminal branch of the anterior division of the internal 

 iliac. It is directed downward in front of the sciatic artery to the lower portion of the 

 great sacro-sciatic foramen, where it makes its exit from the pelvis, passing between 



