STRUCTURE OF THE INTESTINAL CANAL. 509 



the left sacroiliac 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 

 knver extremity, previously to its termination at the anus, forms a dilata- 

 tion of considerable but variable magnitude. 



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

 tions ; 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 inter- 

 nal iliac artery, and with the sacral plexus of nerves ; one or tw r o convo- 

 lutions of the small intestine are interposed 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, vesicular 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 separated 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 Jlnus is situated at a little more than an inch in front of the ex- 

 tremity 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 faces. The margin of the anus is provided with an abun- 

 dance of sebiparous glands, and the epiderma 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, de- 

 rived from the peritoneum. 



Mucous COAT. The mucous membrane of the mouth invests the whole 

 internal surface of that cavity, and is reflected along the parotid, submax- 

 illary, and sublingual ducts, into the corresponding glands. It terminates 

 anteriorly upon the outer margin of the red border of 'the lips, and poste- 

 riorly is continuous with the mucous lining of the pharynx. The mucous 

 membrane of the pharynx is continuous with the mucous lining of the 

 Eustachian tubes, the nares, the mouth, and the larynx. In the oesopha- 

 gus it is thick, very loosely connected with the muscular coat, and disposed 

 in longitudinal plica. In the stomach the mucous membrane is thin and 

 43* 



