Tin: llECTl'M AM) A XL'S 97.') 



Tho two roiniiiniiii^ ])()rti()iis of the intestine extend I'roui tlic niiiMIe of tlu' lliinl 

 piece of the sacrum to the anus. 



It would be well if the term ' rectum ' were to be limited to that part of the 

 bowel which is below the level of the third segment of the sacrum, and which is 

 free of an}'^ meso-colon. This ])ortion of bowel — the rectum proper — may l)e 

 divided into two i)ortions. Tlie lirst i)ortion extends from thi' tliird ])i(ce of the 

 sacrum to tlio tij) of the ct)ccyx. 



This i)ortion, about three and a half in(^hes long, is only covered by peritoneum 

 above, and then only over the anterior surface. Behind, it is in relation with the 

 sacrum and coccyx. In front it is in relation with the trigone of the bladder, the 

 vesiculie seminales, and under surface of the prostate. In tlie female the anterior 

 surface is in relation with tlie vagina and the cervix uteii. 



The peritoneum is reflected from the rectum to the bladder in the male, and 

 the vagina in the female (recto-vesical or recto-vaginal pouch). This pouch 

 extends in the male to witliin al)out three inches of the anus. On the posterior 

 surface of the gut there is no peritt)neum below a i)oint five inches from the anus. 



The second portion (or what used to be called the tliird portion) extends from 

 the tip of the coccyx to the anus; it is about an inch and a half long. It differs 

 from the first portion in the direction of its curve: while that follows the curve of 

 the sacrum and coccyx, this portion turns backwards and downwards. It is not 

 connected with the peritoneum. It is surrounded, after leaving the prostate, by the 

 internal sphincter, while the levator ani is attached to its side. At its end the 

 external spliincter is situated; in front is the triangular ligament of the perineum. 

 Just aI)ove the anus the n.'ctum is much dilated. 



The anus. — The anus is the aperture l)y which the intestine opens externally. 

 During life it is contracted by the sphincters, so as to give the skin around a 

 wrinkled a])pearance. Round the lower part of the rectum and anus certain 

 muscles that are connected with its proi:)er function are situated. They are the 

 internal sphincter, the levator ani, and the external sphincter. The levator ani 

 and external sphincter will be found described in another part. 



The internal sphincter is a thickening of the circular fibres of the intestine, 

 situated round the rectum about an inch above the anus, and extending over half 

 an inch of the intestine. It forms a complete muscular ring. It is two lines thick, 

 and is paler than tlie external sphincter. 



The rectum differs from the rest of the colon in presenting perfectly smootli 

 walls marked ))V no sacculi, by no longitudinal muscular liands, and by no ap])en- 

 dices. The mucous membrane of the rectum is thicker than that of the rest of the 

 large intestine. Certain folds, chiefly longitudinal in direction, are seen in the lax 

 state of the tube, which disappear when distended. Houston has described three 

 oblique semilunar folds, which project into the lumen of the tube: one in front l>y 

 the ])rostate, and two others higher up; one from the left side, and one on the 

 right, the highest. 



Structure of the large intestine. — Tliere are four coats: a serous, muscular, 

 mui'ous, and submucous. 



The serons is derived from the peritoneum, and is more or less (■om])lete. 



The appendices cpiploicse in conneetion with this laver liave lieen mentioiu'd 

 (fig. 576). 



The muscular coat is divided into circular and longitudinal layers, the longi- 

 tudinal being external. The arrangement of the longitudinal fibres has been 

 described in as far as they make up th(! three longitudinal ])ands (fig. 576). Only 

 a small amount of longitudinal fibres arc found between the l)ands, except on thi' 

 vermiform appendix and lower part of the sigmoid llexure, where they an- 

 arranged all round. 



The circular iibres form a thin layer, and are mostly collected in the interval 

 between the sacculi. 



The mucoKS mnnhrnne, se])arated from the muscular lavfr by the Kuhmiiroii.^ 

 layer, has no villi, and no valvuhe coimiventes. 



Blood-vessels. — The large inti'stine is su]i])lied with blood by the branches of 

 the su])erior mesenteric and inferior mesenteric arteries, while it also receives a 

 l)lood-supi)ly from the internal iliac at the rectum. The vessels form a continuotis 



