368 



STOMACH AND INTESTINE. 



which generally concedes to the contents of 

 the large intestine a long delay, and a slight 

 movement over a large absorptive surface, 

 would still be quite capable of effecting their 

 rapid and vigorous expulsion, when required 

 to do so. Nay, more, since much of this ex- 

 pulsive act seems, as it were, removed from 

 the sacculi themselves, and concentrated in 

 the bands around them, we may conjecture 

 that the mechanism of these latter contrac- 

 tile masses is also specially concerned in the 

 nervous part of the process. At least, it is 

 not impossible, that the irritation or stretching 

 of these two sets of muscles (which can be 

 effected only by the general distention of the 

 calibre of the tube, and not by the local dis- 

 tention of its cells) may constitute the im- 

 mediate stimulus of the evacuation of the 

 whole large intestine, or of any particular 

 segment. 



The mucous membrane of the colon may be 

 described as only differing from that of the 

 small intestine in the fact that it is somewhat 

 thicker, and quite devoid of villi. Its more 

 numerous tubes are about one-third longer 

 than those of the small intestine ; and their 

 diameter seems to be, in genera!, still more 

 increased. Its solitary follicles are also more 

 numerous, and of larger size. And the 

 depressions which mark the site of each on 

 the internal surface of the bowel are here 

 represented by a distinct pit ; which leads by 

 vertical, or even somewhat divergent sides, 

 to the follicle that occupies its base. But the 

 secretions of these structures, and the cell- 

 growth which lines them, do not present any 

 noticeable difference from their analogues in 

 the small intestine. 



The rectum (/-, fg. 274. ; r 1, r 2, r 3, Jig. 

 276.) (formerly straight gut, Eng. ; Mastdarm, 

 Germ.), which intervenes between the sig- 

 moid flexure of the colon (s) and the anus 

 (w), forms the terminal segment of the large 

 intestine. It has received the above name 

 from the comparatively direct course which 

 it takes. Its length is about seven to eight 

 inches. Its width is at first only equal to 

 that of the small extremity of the colon, 

 with which it is continuous : but gradually 

 increases, so as to form a kind of dilatation or 

 pouch in the immediate neighbourhood of its 

 lower aperture. Here it suddenly contracts 

 to the narrow orifice of the anus ; which is 

 situated in the perineal space, that closes the 

 pelvis, and forms the lower extremity of the 

 trunk. 



Strictly speaking, however, the rectum is 

 by no means straight. Beginning at the left sa- 

 cro-iliac symphysis (e,fig. 276.), it first passes 

 obliquely downwards and to the right side, 

 towards the median line of the trunk; which 

 it reaches at a point that nearly corresponds 

 to the body of the third sacral vertebra (at 

 r 1, fig. 276.). And though, from hence to 

 its termination, it continues to occupy the 

 middle line, still as it rests upon the concave 

 anterior surface of the remainder of the spinal 

 column, it assumes a curve similar to that of 

 the sacrum. It thus acquires a second and 



more remarkable bend (at r 2, Jig. 276.), which 

 is convex backwards. Finally, at the tip of the 

 coccyx, it quits the antero-posterior direction 

 given it by this bone ; and, bending suddenly 



Fig. 276. 



The viscera of the adult male pelvis, as seen after 

 the removal of the right innominate bone : show- 

 ing the situation and relations of the rectum. 



a, fourth lumbar vertebra; b, bladder; c, sym- 

 physis of the pubis ; d, inner surface of the left 

 osilii; e, sacro-iliac articulation;/, vasdeferens; 

 g, ureter ; h, spine of the ischium sawn through, 

 and left attached by the coccygeus muscle ; i, left 

 vesicula seminalis; " k, prostate gland; /, bulb of 

 the urethra ; m, left corpus .caveruesum divided at 

 its root ; n, anus ; o, levator ani cut across near its 

 attachment to the coccyx ; p. sciatic nerves and 

 vessels ; 9, fibres of levator ani passing round the 

 lower end of the rectum ; r, rectum, 1, 2, 3, its first, 

 second, and third portions ; s, sigmoid flexure of 

 the colon ; r v, peritoneum forming the left side 

 of the recto-vesical pouch. 



downwards at a right angle, becomes vertical 

 for a very short distance (at r 3, Jig. 276.) prior 

 to ending in the anus. 



The above successive changes in its di- 

 rection are associated with others, which af- 

 fect its relations to the peritoneum and to the 

 surrounding structures. In accordance with 

 these, it is usual to describe the rectum as 

 subdivided into three portions. 



The first or oblique segment (between s 

 and r 1, fig. 276.) is about 3 inches long. 

 It is covered on every side by peritoneum ; 

 which, at its commencement, attaches it to 

 the pelvis by a short meso-rectum, very simi- 

 lar to the meso-colon of the sigmoid flexure.* 

 It lies on the sacrum, the upper border of 

 the pyriformis muscle, and the sacral plexus. 

 In front of it is the bladder, from which it 

 is generally separated by some convolu- 

 tions of the small intestine. On either side 



* This meso-rectum is sometimes so long, as to 

 give this segment of the bowel a mobility (and often 

 a shape) very similar to that of the neighbouring 

 sigmoid flexure itself. 



