458 



ABDOMEN 



submucous coat they proceed down to the anal canal, where 

 it is usual to find one within each rectal column (p. 466). 

 The terminal twigs anastomose freely with each other and 

 with branches of the middle and inferior haemorrhoidal 

 arteries. 



Arteria Sacralis Media. 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 

 lowest two lumbar vertebrae and behind the left common 

 iliac vein. Reaching the sacrum, it continues downwards in 

 the median plane to the tip of the coccyx. It supplies the 

 glomus coccygeum, 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 deep 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 around the prostate, bladder, and rectum are 

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

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

 static] and prostatico-vesical plexuses have already been noticed ; 

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

 The hamorrhoidal pkxus consists of two parts, one in the 

 submucous 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 hamor- 

 rhoidal vein, which ends in the inferior mesenteric vein ; 

 the middle Juzmorrhoidal veins, which end in the hypo- 

 gastric veins ; and the inferior Juzmorrhoidal veins, which 

 go to the internal pudendal veins. The hsemorrhoidal 

 plexus is therefore a link between the portal and systemic 

 systems of veins. This is of practical importance in associa- 

 tion with the production of haemorrhoids or piles, which are 

 due to a varicose condition of the haemorrhoidal veins. The 

 portal vein and its larger tributaries are without valves ; con- 

 sequently, anything which retards the flow of blood through 

 the portal system will react upon the haemorrhoidal plexus, 



