LARGE INTESTINE. 739 



The Rectum is the terminal part of the large intestine, and extends from the 

 sigmoid flexure to the anus; it varies in length from six to eight inches, and 

 has received its name from being less flexuous than any other part of 'the 

 intestinal canal. It commences opposite the left sacro-iliac symphjsis, passes 

 obliquely downwards from left to right to the middle of the sacrum, forming a 

 gentle curve to the right side; then, regaining the middle line, it descends in 

 front of the lower part of the sacrum and coccyx, and, near the extremity of the 

 latter bone, inclines backwards to terminate at the anus, being curved both 

 in the lateral and antero- posterior directions. The rectum is, therefore, not 

 straight, the upper part being directed obliquely from the left side to the me-, 

 dian line, the middle portion being curved in the direction of the hollow of the 

 sacrum and coccyx, and the lower portion presenting a short curve in the oppo- 

 site direction. The rectum is cylindrical, not sacculated like the rest of the 

 large intestine; it is narrower at its upper part than the sigmoid flexure, gra- 

 dually increases in size as it descends, and immediately above the anus presents 

 a considerable dilatation, capable of acquiring an enormous size. The rectum 

 is divided into three portions, upper, middle, and lower. 



The upper portion, which includes about half the length of the tube, extends 

 obliquely from the left sacro-iliac symphysis to the middle of the third piece 

 of the sacrum. It is almost completely surrounded by peritoneum, and con- 

 nected to the sacrum behind by a duplicature of that membrane, the meso-rectum. 

 It is in relation behind with the Pyriformis muscle, the sacral plexus of nerves, 

 and the branches of the internal iliac artery of the left side, which separate it 

 from the sacrum and sacro-iliac symphysis ; in front it is separated, in the male, 

 from the posterior surface of the bladder: in the female, from the posterior 

 surface of the uterus, and its appendages, by some convolutions of the small 

 intestine. 



The middle portion of the rectum is about three inches in length, and extends 

 as far as the tip of the coccyx. It is closely connected to the concavity of the 

 sacrum, and covered by peritoneum only on the upper part of its anterior sur- 

 face. It is in relation, in front, in the male, with the triangular portion of the 

 base of the bladder, the vesiculaa seminales, and vasa deferentia ; more anteri- 

 orly, with the under surface of the prostate. In the female, it is adherent to 

 the posterior wall of the vagina. 



The lower portion is about an inch in length ; it curves backwards at the fore 

 part of the prostate gland, and terminates at the anus. This portion of the in- 

 testine receives no peritoneal covering. It is invested by the Internal Sphinc- 

 ter, supported by the Levatores Ani muscles, and surrounded at its termination 

 by the External Sphincter. In the male, it is separated from the membranous 

 portion and bulb of the urethra by a triangular space ; and, in the female, a 

 similar space' intervenes between it and the vagina. This space forms by its 

 base the perineum. 



Structure. The large intestine has four coats : serous, muscular, cellular, and 

 mucous. 



The serous coat is derived from the peritoneum, and invests the different por- 

 tions of the large intestine to a variable extent. The caecum is covered only 

 on its anterior surface and sides ; more rarely, it is almost completely invested, 

 being held in its position by a duplicature, the meso-csecum. The ascending 

 and descending colon are usually covered only in front. The transverse colon 

 is almost completely invested, the parts corresponding to the attachment of the 

 great omentum and transverse meso-colon being alone excepted. The sigmoid 

 flexure is nearly completely surrounded, the point corresponding to the attach- 

 ment of the sigmoid meso-colon being excepted. The upper part of the rectum 

 is almost completely invested by the peritoneum: the middle portion is covered 

 only on its anterior surface ; and the lower portion is entirely devoid of any 

 serous covering. In the course of the colon, and upper part of the rectum, the 



