THE INTERNAL ILIAC ARTERY. 8ii 



with the other spinal arteries. The inferior artery passes at first inward and then 

 downward upon the surface of the sacrum, parallel to the middle sacral artery, with 

 which it anastomoses at the tip of the coccyx and also, by delicate transverse branches, 

 opposite each sacral vertebra. Opposite each anterior sacral foramen that it passes 

 — i.e., opposite the second, third, and fourth — it gives off a branch (ramus spinalis) 

 which enters the foramen and behaves like the spinal branch of the superior artery. 

 In its downward course the inferior lateral sacral lies to the outer side of the sacral 

 portion of the sympathetic cord and crosses the slips of origin of the pyriformis 

 muscle. 



Variations. — Very frequently the two lateral sacral arteries arise by a common stem, and 

 occasionally the branch which enters the second anterior sacral foramen arises independendy. 

 In-all probability the longitudinal stem of the inferior artery is to be regarded as having been 

 formed by the direct anastomosis of ascending and descending twigs from the lateral branches 

 of the middle sacral, each of which is serially homologous with the lumbar and intercostal arte- 

 ries. The process is similar to what has occurred in the formation of the vertebral artery 

 (page 721). 



3. The Gluteal Artery. — The gluteal artery (a. glutaea superior) (Fig. 727) is 

 the continuation of the posterior division of the internal iliac. It is the largest of all 

 the branches of that vessel, and passes backward between the lumbo-sacral cord and 

 the first sacral nerve to the upper border of the great sacro-sciatic foramen. It passes 

 through the foramen, in company with the superior gluteal nerve, above the pyriformis 

 muscle, and soon after making its exit from the pelvis divides into a superficial and a 

 deep branch. 



Branches. — (a) The superficial branch (ramus superior) soon divide, mto a number of 

 branches which enter the upper portion of the gluteus maximus, some supplying that mugcle, 

 while others traverse it to supply the skin over the upper part of the gluteal region. One 

 branch, larger than the others, passes outward along the upper border of the origin of the 

 gluteus medius almost to the anterior superior spine of the ilium, anastomosing with branches of 

 the external circumflex iliac artery. 



{b) The deep branch (ramus inferior) soon divides into two branches, {aa) The superior 

 branch passes outward along the upper border of the gluteus minimus almost to the anterior 

 inferior spine of the ilium, where, under cover of the tensor vaginae femoris, it anastomoses 

 with the descending branch of the external circumflex iliac ; it sends branches to both the glu- 

 teus medius and minimus, {bb) The inferior branch passes outward and downward, over the 

 surface of the gluteus medius, towards the greater trochanter of the femur, and gives branches 

 to both the gluteus medius and minimus and to the hip-joint. 



4. The Superior Vesical Artery. — The superior vesical artery (a. umbilicalis) 



(Fig. 724) represents the original main stem of the foetal hypogastric artery, and 

 consequently takes its origin from the hypogastric axis and is continuous anteriorly 

 with the fibrous cord which represents the obliterated hypogastric artery (Fig. 728). 

 It passes forward, beneath the peritoneum, towards the urinary bladder, and as it 

 approaches that structure gives off branches to it (aa. vesicales superiores) which ramify 

 over its surface and sides and supply its upper and middle portions. They anasto- 

 mose below with branches of the prostatic and inferior vesical arteries. 



Variations.— Not infrequently an accessory branch arising from the superior vesical is dis- 

 tributed to the middle and lower portions of the bladder, forming what has been termed the 

 middle vesical artery ( Fig. 724) . 



5. The Inferior Vesical Artery. — The inferior vesical artery (a. vesicalis 

 inferior) (Fig. 724) may arise from the hypogastric axis, from the anterior division of 

 the internal iliac below^ the axis, from the middle hemorrhoidal, or quite frequently 

 from the prostatic. It descends towards the lower portion of the bladder, supplying 

 the base and neck of that structure, and also sending branches to the prostate gland 

 and the seminal \'esicles in the male. It anastomoses with branches of the prostatic 

 and superior vesical arteries. 



Variations. — The inferior vesical is usually a rather slender branch, and may be replaced 

 by vesical branches from the prostatic or by branches of the superior vesical. 



