THE ABDOMEN 623 



The third part is the part of the vessel which lies on the outer 



wall of the ischio-rectal fossa. It is here contained in Alcock's 

 canal, and is situated about i^ inches above the lower part of the 

 tuber ischii. For its relations see Alcock's canal. 



Branches. — ^These are as follows : the inferior hemorrhoidal, the 

 superficial perineal, and the transverse perineal. 



The inferior hemorrhoidal artery arises, either singly or in two 

 or three branches, from the internal pudic immediately after it 

 has taken up its position in Alcock's canal. The branches pass 

 inwards to the anal canal through the loose fat which fills the 

 ischio-rectal fossa. They are distributed to the external sphincter, 

 levator ani, wall of the anal canal, and superficial structures of 

 one half of the ischio-rectal division of the perineum, and they 

 anastomose with the middle and superior hemorrhoidal arteries, 

 and the inferior hemorrhoidal branches of the opposite side. 



The superficial perineal artery arises from the internal pudic at 

 the anterior part of the ischio-rectal fossa. It pierces the base of 

 the antero-inferior layer of the triangular ligament, and passes 

 superficial to (sometimes on the deep surface of) the superficial 

 transverse perineal muscle. Its subsequent course is forwards 

 under cover of the fascia of Colles, where it lies in the floor of the 

 deep perineal triangle, in company with the three long scrotal 

 nerves. On approaching the scrotum it di\ddes into several long 

 slender branches, which supply the back of the scrotum and 

 anastomose with the external pudic branches of the common 

 femoral artery. 



The transverse perineal artery, as a rule, arises in common with 

 the superficial perinccJ, of which it is sometimes regarded as a 

 branch. It may, however, arise directly from the internal pudic 

 immediately in front of the origin of the superficial perineal. It 

 is directed inwards and forwards to the central tendinous point 

 lying superficial to the superficial transverse perineal muscle, and 

 beneath the fascia of Colles. It supplies the muscles which meet at 

 the central tendinous point, and anastomoses with its fellow of the 

 opposite side. 



Alcock's Canal. — ^This canal is situated in the outer wall of the 

 ischio-rectal fossa, and is formed by the obtiuator fascia. Its 

 contents from below upwards are as foUows : (i) the perineal 

 division of the pudic nerve ; (2) the lower vena comes ; (3) the 

 third part of the internal pudic artery ; (4) the upper vena comes ; 

 and (5) the dorsal nerve of the penis. 



The fourth part of the internal pudic artery lies between the two 

 layers of the triangular ligament. It enters this interspace by 

 piercing the postero-superior layer of that ligament close to its base 

 and near the ischial ramus. It is embedded in the compressor 

 urethrae muscle, and is comparatively superficial. As it Ues near 

 the ischio-pubic ramus it has a vena comes on either side of it, and 

 the dorsal nerve of the penis is external to it. 



Branches. — ^These are as follows : the artery of the corpus 



