THE INTERNAL ILIAC ARTERY. 817 



the pyriformis and coccygeus muscles. It then bends forward, under cover of the 

 gkiteus maximus, and, curving beneath the spine of the ischium, passes through the 

 lesser sacro-sciatic notch to enter the ischio-rectal fossa. Its course is then forward 

 along the lateral wall of the fossa, lying with its accompanying vein and the pudic 

 nerve in a fibrous canal known as Alcock' s canal, formed by a splitting of the obtu- 

 rator fascia near its lower border. At the anterior portion of the ischio-rectal fossa 

 the artery perforates the triangular ligament of the perineum and passes forward 

 between the two layers composing that structure, finally perforating the superficial 

 layer and becoining the dorsal artery of the penis (or chtoris). 



Branches. — In the pelvic and gluteal portions of its course the internal pudic, as a rule, 

 gives off only slender muscular branches to the neighboring muscles, hi its ischio-rectal por- 

 tion its branches are more important. 



(a) The inferior hemorrhoidal arteries (aa. haemorrhoidales inferiores), usually two in num- 

 ber, but frequent!)- only one, which early divides into two or three stems, arise from the internal 

 pudic, just after it has traversed the lesser sacro-sciatic foramen. They perforate the inner wall 

 of Alcock' s canal and pass through the fat-tissue which occupies the ischio-rectal fossa towards 

 the lower part of the rectum. They give branches to the ischio-rectal fat-tissue, to the sphincter 

 and levator am, to the gluteus maximus, to the skin over the ischio-rectal and anal regions, and 

 to the lower part of the rectum, anastomosing above with the middle hemorrhoidal branches of 

 the internal iliac. 



((?>) The superficial perineal artery (a. perinei) arises just before the internal pudic enters the 

 space between the layers of the triangular ligament of the perineum. It is at first directed 

 almost vertically downward, but quickly bending around the posterior border of the superficial 

 transverse muscle of the perineum, near its origin from the ischial tuberosity, it is directed for- 

 ward and inward in the interval between the ischio-cavernosus and bulbo-cavernosus muscles. 

 In this portion of its course it is covered only by the superficial perineal fascia and the integu- 

 ment, and passes forward to be distributed to the posterior portion of the scrotum in the male 

 and to the labia majora in the female. In its course it gives off numerous cutaneous branches 

 as well as branches to the neighboring muscles. One of these latter, usually somewhat larger 

 than the rest, passes inward towards the median line, beneath the superficial transverse muscle 

 of the perineum, which it supplies, as also the bulbo-cavernosus and external sphincter ani. 

 This is what has been termed the transverse artery of the perineui)i. It anastomoses at the 

 central point of the perineum with its fellow of the opposite side, with other branches from the 

 superficial perineal artery anteriorly and with branches of the inferior hemorrhoidals posteriorly. 



In its perineal portion also the internal pudic gives off important branches. 



(r) The artery to the bulb (a. bulbi urethrae or a. bulbi vestibuli) arises from the internal 

 pudic a short distance after it has entered the deep perineal interspace. It is a relatively 

 large vessel in the male, and passes almost horizontally inward towards the median line. 

 Before reaching this, however, it perforates the superficial layer of the triangular ligament, 

 enters the substance of the bulbus urethrae about 15 mm. in front of its posterior extremity, 

 and is distributed to that structure and to the posterior third of the corpus spongiosum and 

 urethra. In the female it is of a lesser calibre than in the male, and is distributed to the bulbus 

 vestibuli. 



{d) The urethral artery (a. urethralis) arises usually some distance anteriorly to the artery 

 of the bulb, and, like it, is directed medially, and penetrates the superficial layer of the tri- 

 angular ligament to enter the substance of the corpus spongiosum. It reaches the corpus 

 spongiosum just behind the symphysis pubis, where the two corpora cavernosa come together 

 to form the penis, and is continued forward in the spongiosum to the glans. It is a somewhat 

 inconstant branch, and is quite small in the female. 



(e) The artery of the corpus cavernosum fa. profunda penis s. clitoridis) arises from the 

 internal pudic, jUSt posterior to the lower border of the symphysis pubis, and is directed 

 outward towards the bone. It penetrates the superficial layer of the triangular ligament 

 close to its attachment to the pubic ramus, and enters the corpus cavernosum at about the 

 junction of its middle and posterior thirds. It passes to the centre of the corpus and there 

 divides into a posterior branch which supplies blood to the posterior third of that structure, 

 and an anterior one which distributes to its anterior two-thirds. It is much smaller in the 

 female than in the male. 



if) The dorsal artery of the penis or clitoris (a. dorsalis penis s. clitoridis) is the continua- 

 tion of the main stem of the internal pudic beyond the origin of the artery to the corpus cav- 

 ernosum. It penetrates the superficial layer of the triangular ligament near its apex, and passes 

 upward in the suspensory ligament of the penis or clitoris to the dorsal surface of that organ, 

 along which it passes, lying to the side of the median line and separated from its fellow of the 

 opposite side bv the single median dorsal vein. Laterally to it is situated the dorsal nerve of 



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