294 Anatomy Applied to Medicine and Surgery. 



rhoidal veins are the vessels affected. These two sets 

 of venous radicles, i.e., the inferior hemorrhoidal on 

 the one hand, and the superior and middle on the other, 

 communicate just within the anal margin, and this con- 

 nection between the portal and caval systems affords an 

 outlet for the rectal vessels that are distended from obstruc- 

 tion of the portal vein. Hence, in "piles," it is advisable to 

 bear in mind the fact that instead of being a purely local 

 affair, the venous distention may be symptomatic of dis- 

 ease of the liver, or of the portal vein itself, whereby re- 

 sistance is offered to the circulation through the portal 

 channels. Should tenesmus be a symptom of the pre- 

 sence of "piles," it is dependent on the irritation of the 

 sensory nerves of the lower part of the rectum, being re- 

 ferred, through a centre in the lumbar region of the spinal 

 cord, to the plexus mesentericus of the intestine, and 

 causing peristalsis, while at the same time, reflex stimula- 

 tion of the sphincters causes their contraction. 



Fissure in Ano. In this condition a tear is present in 

 the muco-cutaneous margin of the anus, and hence, the 

 distention of the orifice, that, normally, occurs during the 

 act of defcecation, irritates filaments of the inferior 

 hemorrhoidal nerve that may be exposed in the 

 base of the fissure, with the result, that the reflex 

 act, which, normally, contracts the sphincter for 

 some time after a stool, becomes converted into the 

 pathological condition of persistent contraction. This is 

 probably due to the irritation of the exposed nerve being 

 transferred through the lumbar centre to the branch of 

 the fourth sacral supplying motion to the sphincter ani 

 muscle, and since this spastic condition of the sphincter 

 muscles still further irritates the exposed nerve, it follows, 

 that pain may persist, oftentimes for hours, after the 

 act of defoecation. Again, the effects of this irritation of 



