08 THE BLOOD-VASCULAR SYSTEM 



foramen, and is distributed to the skin over the back of the sacrum, there anas- 

 tomosing with branches of the superior and inferior gluteal arteries. The inferior 

 lateral sacral descends on the side of the sacrum, lateral to the sacral chain of the 

 sympathetic, and medial to the anterior sacral foramina, crossing in its course the 

 slips of origin of the piriformis muscle and the first anterior sacral nerve. On 

 reaching the coccyx it anastomoses in front of that bone with the middle sacral 

 artery, and with the inferior lateral sacral of the opposite side (fig. 489). 



In this course it gives off: — Spinal branches [rami spinales], which enter the second, third 

 and fourth anterior sacral foramina, and, after supplying the spinal membranes and anastomos- 

 ing with each other, leave the spinal canal by the corresponding posterior sacral foramina, and 

 are distributed to the muscle and skin over the back of the sacrum; and rectal branches which 

 run forward to the rectum. 



At times the lateral sacral arteries are exceedingly small, the spinal branches then coming 

 chiefly from the middle sacral. The anastomosing branches between the lateral sacral and 

 middle sacral are usually regarded as sacral arteries diminished in size, and serially homologous 

 with the lumbar and intercostal arteries. 



3. THE OBTURATOR ARTERY 



The obturator artery [a. obturatoria], usually arises from the anterior division 

 of the h3^pogastric. It runs forward and downward a little below the brim of the 

 pelvis, having the obturator nerve above and the obturator vein below. It here 

 lies between the peritoneum and the endo-pelvic fascia, but later it passes through 

 the obturator canal, the aperture in the upper part of the obturator membrane. 

 In this course it is crossed by the ductus deferens. On emerging from the obturator 

 canal the artery divides into two branches, anterior and posterior, which wind 

 around the margin of the obturator foramen beneath the obturator externus 

 muscle. 



The branches of the obturator artery are: — (1) The iliac or nutrient branch; 

 (2) a vesical branch; (3) the pubic branch; (4) the anterior, and (5) posterior 

 terminal branches. 



(1) The iliac or nutrient branch ascends to the iliac fossa, passing between the iliacus 

 muscle and the bone. It suppUes a nutrient vessel to the iUum, and anastomoses with the 

 medial branch of the iliac division of the ilio-lumbar artery. 



(2) The vesical branch or branches are smaU vessels which run in the lateral false ligament 

 of the bladder to that organ, where they anastomose with the other vesical arteries. 



(3) The pubic branch [ramus pubicus] comes off from the obturator as that vessel is leaving 

 the pelvis by the obturator canal. It runs upward and medially behind the pubis, anastomosing 

 with its fellow of the opposite side of the body, and with the pubic branch of the inferior epi- 

 gastric artery. One of the anastomosing channels between the pubic branch of the obturator 

 and pubic branch of the inferior epigastric arteries is sometimes of large size, a fact of surgical 

 interest in that the enlarged vessel may then run around the medial side of the femoral ring 

 (pp. 615 and 636). 



(4) The anterior branch [ramus anterior] runs around the medial margin of the obturator 

 foramen, and anastomoses with the posterior branch and with the medial circumflex artery . It 

 supplies branches to the obturator and adductor muscles. 



(5) The posterior branch [ramus posterior] skirts the lateral margin of the obturator fora- 

 men, lying between the obturator externus and the obturator membrane. At the lower margin 

 of the foramen it divides into two branches. One branch continues its course around the lower 

 margin of the foramen, and anastomoses with the anterior branch of the obturator and with 

 the medial circumflex. The other branch turns laterally below the acetabulum, and ends in the 

 muscles arising from the tuberosity of the ischium. It anastomoses with the inferior gluteal 

 artery. This branch gives off a small twig, the acetabular artery [a. acetabuli], which passes 

 under the transverse ligament into the hip-joint, where it supplies the synovial membrane, 

 the ligamentum teres, and the fat in the fossa at the bottom of the acetabulum. 



4. THE GLUTEAL ARTERIES 



There are two gluteal arteries, the superior and inferior. The superior 

 gluteal artery [a. glutea superior], the largest branch of the posterior division of 

 the hypogastric comes off as a short, thick trunk from the lateral and back part 

 of that vessel, of which indeed it may be regarded as the continuation. Passing 

 backward between the first sacral nerve and the lumbo-sacral trunk through an 

 osseo-tondinous arch formed by the margin of the bone and the upper edge of the 

 endo-polvic fascia, it loaves the pelvis through the great sciatic foramen above 

 the piriformis muscle in company with its vein and the superior gluteal nerve. At 

 its exit posteriorly from the great sciatic foramen it lies under cover of the gluteus 



