602 ABDOMEN 



third piece of the sacrum. There it divides into two 

 branches which proceed downwards, one on either side of the 

 rectum. Each of these branches soon breaks up into smaller 

 branches, which range themselves round the gut and pierce 

 its muscular coat about the middle of its length. Within the 

 submucous coat they proceed down to the anal canal, where 

 it is usual to find one within each rectal column (p. 610). 

 The terminal twigs anastomose freely with each other and 

 with branches of the middle and inferior haemorrhoidal 

 arteries. 



Arteria Sacralis Media (Middle Sacral Artery). During 

 the dissection of the abdomen the middle sacral artery was 

 seen springing from the back of the termination of the aorta 

 above the common iliac arteries. It descends in front of 

 the bodies of the lower two lumbar vertebrae and behind the 

 left common iliac vein. Reaching the sacrum, it continues 

 downwards in the medial plane to the tip of the coccyx. 

 It supplies the coccygeal body, and, from each side, it gives 

 off small twigs which anastomose with the lateral sacral 

 arteries. 



Veins of the Pelvis. The arrangement of the veins in 

 the pelvis corresponds in great measure to that of the 

 arteries ; but there are some important differences, viz. : 



(1) The dorsal vein of the penis, instead of joining the 

 internal pudendal vein, enters the pelvis and divides into two 

 branches, which join the pudendal plexus of veins. 



(2) The ilio-lumbar and middle sacral veins pour their 

 blood, as a rule, into the common iliac veins. 



(3) The veins round the prostate, bladder, and rectum are 

 large and numerous, and form dense plexuses, which com- 

 municate freely with each other. The pudendal (O.T. 

 prostatic] and vesical plexuses have already been noticed ; the 

 blood is drained from them chiefly by the vesical veins. The 

 hczmorrhoidal plexus consists of two parts, one in the sub- 

 mucous coat and one on the surface of the gut. It is the 

 latter which is seen in the dissection. The blood is drained 

 from it by three groups of channels, viz. the superior hczmor- 

 rhoidal vein, which ends in the inferior mesenteric vein ; 

 the middle hczmorrhoidal veins, which end in the hypo- 

 gastric veins ; and the inferior hcemorrhoidal veins, which 

 go to the internal pudendal veins. The haemorrhoidal 

 plexus is therefore a link between the portal and systemic 



