568 STRUCTURE OF THE INTESTINAL CANAL. 



The Rectum is the termination of the large intestine. It has re- 

 ceived its name, not so much from the direction of its course, as from 

 the straightness of its form in comparison with the colon. It descends, 

 from opposite the left sacro-iliac symphysis, in front of the sacrum, 

 forming a gentle curve to the right side, and then returning to the 

 middle line ; near the extremity of the coccyx it curves backwards to 

 terminate at the anus at about an inch in front of the apex of that 

 bone. The rectum, therefore, forms a double flexure in its course, the 

 one being directed from side to side, the other from before backwards. 

 It is smaller in calibre at its upper part than the sigmoid flexure, but 

 becomes gradually larger as it descends, and its lower extremity, pre- 

 viously to its termination at the anus, forms a dilatation of consider- 

 able but variable magnitude. 



With reference to its relations, the rectum is divided into three 

 portions ; the first, including half its length, extends to about the 

 middle of the sacrum, is completely surrounded by peritoneum, and 

 connected to the sacrum by means of the meso-rectum. It is in 

 relation above with the left sacro-iliac symphysis, and below with the 

 branches of the internal iliac artery, and with the sacral plexus of 

 nerves ; one or two convolutions of the small intestine are inter- 

 posed between the front of the rectum and the bladder in the male ; 

 and between the rectum and the uterus with its appendages in the 

 female. The second portion, about three inches in length, is closely 

 attached to the surface of the sacrum, and covered by peritoneum only 

 in front ; it is in relation by its lower part with the base of the 

 bladder, vesiculse seminales, and prostate gland, and in the female 

 with the vagina. The third portion curves backwards from opposite 

 the prostate gland to terminate at the anus ; it is embraced by the 

 levatores ani, and is about one inch and a half in length. It is sepa- 

 rated from the membranous portion of the urethra by a triangular 

 space ; in the female this space intervenes between the vagina and the 

 rectum, and constitutes by its base the perineum. 



The Anus is situated at a little more than an inch in front of the 

 extremity of the coccyx. The integument around it is covered with 

 hairs, and is thrown into numerous radiated plaits which are obliterated 

 during the passage of faeces. The margin of the anus is provided with 

 an abundance of sebaceous glands, and the epidermis may be seen 

 terminating by a fringed and scalloped border, at a few lines above 

 the extremity of the opening. 



STRUCTURE OF THE INTESTINAL CANAL. 



The pharynx has three coats ; a mucous coat, a fibrous coat derived 

 from the pharyngeal fascia, and a muscular layer. The oesophagus 

 has but two coats, the mucous and muscular. The stomach and 

 intestines have three, mucous and muscular, and an external serous 

 investment, derived from the peritoneum. 



