1224 



THE DIGESTIVE SYSTEM. 



a series of small sacculations. The sacculations disappear, and the longitudinal fibres, although 

 thicker in front and behind, form a continuous layer all round, as the rectum proper is 

 approached. 



INTESTINUM RECTUM. 



Intestinum Rectum. The rectum is the portion of the large bowel which 

 intervenes between the pelvic colon above and the anal canal the slit-like 

 passage through which it communicates with the exterior (Fig. 961). 



Unlike the portion of the bowel which immediately precedes it, the rectum has 

 but a partial covering of peritoneum, and is entirely destitute of a mesentery ; 

 sacculations, too, which are so characteristic of the large intestine, cannot properly 

 be said to be present. 



The rectum begins at the termination of the pelvic mesocolon, namely, about the 



Posterior superior spine 



Upper lateral inflexion 

 Peritoneum (pararectal 



Superior hsemorrhoidal 



artery 



Rectur 



Sacro-tuberous ligament 

 Ischio-rectal fossa 



Anal canal 

 Anus 



Third sacral vertebra 



Fourth sacral vertebra 



(cut) 



Lower border of 



piriformis (cut) 



Superior heemorrhoidal 

 artery 



Middle lateral inflexion 

 occygeus 



Levator ani 

 External sphincter 



FIG. 959. THB RBCTUM FROM BEHIND. 



The sacrum has been sawn across through the 4th sacral vertebra, and its inferior part removed with the coccyx. 

 The posterior portions of the coccygei, levatores ani, and of the external sphincter have been cut away. 

 The " pinching in " of the lower end of the rectum by the medial edges of the levatores ani, resulting in the 

 formation of the flattened anal canal, is suggested in the illustration, which has been made from a 

 formalin-hardened male body, aged 30. The lateral inflexions of the rectum, corresponding to the 

 plicae transversales recti, are also shown. 



level of the third sacral vertebra, and ends, where the bowel pierces the pelvic floor, 

 opposite the inferior and posterior part of the prostate in the male, or at a point 

 1J inches (3*7 cm.) in front of, but at a more inferior level than, the tip of the 

 coccyx in both sexes. It first descends along the front of the sacrum and coccyx, 

 following the curve of these bones ; beyond the coccyx, it rests, for about 1 J inches 

 (3*7 cm.), on the posterior part of the pelvic floor, there formed by the union of the 

 two levatores ani ; and finally, having reached the inferior part of the prostate, 

 it bends rather abruptly backwards and downwards, pierces the pelvic floor, 

 and passes into the anal canal (Fig. 959). 



