5*74 THE LARGE INTESTINE. 



it proceeds obliquely downward, in the pelvis, to the mid- 

 dle line of the sacrum, at the lower end of which, accord- 

 ing to Mr. Harrison, it hends forward towards the peri- 

 neum, then backward and downward, to end in the anus, 

 about an inch or more from the coccyx. It presents, there- 

 fore, a curvature both in the lateral and antero-posterior 

 directions. The course of this intestine, however, varies, 

 and, in the foetus, is almost invariably found straight, 

 owing, doubtless, to the straight direction of the spine at 

 that period. 



The size of the rectum varies ; small above, it expands 

 below, just within the anus, into a wide pouch, which is 

 not cylindrical, but flattened in front. In the male the 

 rectum has the bladder, prostate gland, and vesicuhe sem- 

 inales, on its anterior surface ; while, in the female, on the 

 same surface, are the vagina and uterus. 



The peritoneum surrounds this intestine, only at its 

 upper third, fixing it to the sacrum behind, by a reflection 

 termed meso-rectum. In its middle there is only a partial 

 covering in front and at the sides while at its lower por- 

 tion, or inferior third, it is entirely destitute of serous 

 membrane, which is reflected from this point, upon the 

 bladder in the male, and uterus in the female, forming, 

 in each case, a pouch, or cul-de-sac, at the place of re- 

 flection. 



The muscular coat of the rectum increases in thickness/ 

 and exceeds greatly that of any other portion of the intes- 

 tinal canal. The longitudinal layer, which exists as bands 

 in the colon, spreads out and multiplies, and forms a complete 

 tunic for the rectum ; and the circular layer also increases 

 in strength and redness, in its descent, till, at the anus, 

 its fibres become collected in a circular bundle, constituting 

 the internal sphincter ani muscle. There are also some mus- 

 cular fibres, surrounding the anus immediately beneath 

 the integument, termed the external or cutaneous sphincter. 

 Dr. Homer describes the longitudinal fibres, when they 

 have reached the lower border of the internal sphincter, 

 as turning under this border, between it and the external 



