504 STRUCTURE OF INTESTINES. 



turning 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, previously to its termination at 

 the anus, forms a dilatation of considerable but variable size. 



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

 portions; lhe 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 re- 

 lation 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 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, 

 vesiculse seminales, and the 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 leva- 

 tores 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 rec- 

 tum, 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 drawn into numerous radiated plaits which are oblite- 

 rated during the passage of fasces. The margin of the anus is pro- 

 vided with an abundance of sebaceous glands, and the cuticle 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 O3sophagus has but two coats, the mu- 

 cous and muscular. The stomach and intestines have three, mucous 

 and muscular, and an external serous investment, derived 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, submaxillary, and sublingual ducts, into the corresponding 

 glands. It terminates anteriorly upon the outer margin of the red 

 border of the lips, and posteriorly 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 ossophagus it is thick, very 

 loosely connected -with the muscular coat, and is disposed in longi- 

 tudinal plicce, In the stomach the mucous membrane is thin and 



