THE PELVIS 371 



plexus and pierce the muscular coat of the anal canal. They run backwards 

 on the upper surface of the levator ani and join the hypogastric (internal 

 iliac) vein. 



The inferior hcemorrhoidal veins join the internal pudendal vein. 



The anal veins are arranged radially around the margin of 

 the. anus. They communicate with the internal haemorrhoidal 

 plexus and also with the inferior haemorrhoidal veins. Excessive 

 straining during the passage of large scybala may lead to rupture 

 of one of the anal veins, and the extravasated blood gives rise 

 to a small swelling at the muco-cutaneous junction, which is 

 termed an external h&morrhoid. 



Varicosity of the veins of the internal haemorrhoidal plexus 

 constitutes the condition known as internal hemorrhoids. This 

 may be brought about by portal obstruction, whether hepatic 

 or cardiac in origin, since the portal and systemic circulations 

 communicate in the internal hsemorrhoidal plexus (p. 311). 

 Further, the course taken by the superior hsemorrhoidal veins 

 exposes them to marked obstruction during contraction of the 

 muscular coat of the rectum and the downward passage of 

 faeces. This obstruction, together with the absence of venous 

 valves, acts as a predisposing cause of the condition. Internal 

 haemorrhoids may become prolapsed through the anus with 

 each evacuation of the bowels or they may even protrude in 

 the erect posture. Their constriction by the external sphincter 

 gives rise to an acute attack of " piles," and may lead to areas 

 of sloughing or actual gangrene. 



Bleeding from internal haemorrhoids is venous in nature and 

 irregular in occurrence. On the other hand, bleeding from a 

 malignant tumour of the rectum is arterial in nature and occurs 

 with each act of defaecation. 



In the operation for internal haemorrhoids, the clamps or 

 forceps should be applied parallel to the course of the vessels, 

 i.e. in the long axis of the bowel, and special care should be 

 taken to make sure that the vessels at the base of the pile are 

 secured. If this is not done, considerable haemorrhage may 

 occur into the rectum with no outward sign until an enormous 

 blood-clot is passed or the condition of the pulseattraets attention. 



The Nerve -Supply of the Rectum and Anal Canal is 

 mainly derived from S. 2, 3, and 4, through the sympathetic 

 system. The nerves which supply the internal trigone of 

 the bladder and the sphincter vesicae internus are derived 

 from the same source (p. 362). It is not surprising to find 



