STOMACH AND INTESTINE. 



363 



with the large (like the stomach with the duo- 

 denum), opens into it at right angles to its axis, 

 and at some distance from its commencement; 

 so as to leave a blind extremity of the larger 

 tube at the site of their mutual junction. The 

 size of this cnl-dc-sac generally exceeds that of 

 the remainder of the bowel ; it being larger than 

 any other part of the alimentary canal, with 

 the single exception of the stomach. When 

 moderately distended, its diameter ranges from 

 2 to 3 inches ; and its length is about as 

 much. Its vertical extent is, however, somewhat 

 arbitrary ; since, though defined in part of its 

 circumference by the aperture of the ileum 

 and by the ilio-caecal valve, it is elsewhere 

 only limited by an imaginary line drawn 

 around the tube at the level of the latter 

 orifice. 



The situation of the caecum, in the left iliac 

 fossa, allows it to vary considerably in size, 

 without undergoing any marked change of its 

 relations. Bound down as it is to the fascia 

 over the iliacus muscle by peritoneum and 

 loose areolar tissue, its enlargement merely 

 causes it to displace such portions of the small 

 intestine as may hitherto have shared the oc- 

 cupation of the iliac fossa. After its distention 

 has removed these from its anterior surface, 

 it reaches the anterior wall of the belly in the 

 iliac region ; where its size, shape, and con- 

 tents can be more or less recognized during 

 life, by the ordinary means of physical investi- 

 gation. 



The above dimensions render it obvious 

 that the shape of the caecum is somewhat 

 globular. This shape is, however, modified by 

 the arrangement of its muscular layers; which 

 here begin to offer a peculiarity that is main- 

 tained throughout the whole of the colon. The 

 uniform external or longitudinal layer present 

 in the small intestine is here contrasted by one 

 which is separated into three flattened bands, 

 that occupy the side of the tube at nearly equal 

 distances from each other. In the caecum one 

 of these (and the larger of the three) is ante- 

 rior ; one posterior ; and one external. And 

 all three of them become continuous above 

 with the corresponding bands around the as- 

 cending colon. Between these slips of muscle, 

 the bowel presents a more or less dilated and 

 projecting external surface ; which is again sub- 

 divided by transverse constrictions into subor- 

 dinate pouches or sacculi. On laying open the 

 bowel, and removing the mucous membrane 

 from its inner surface, it may be seen that these 

 transverse constrictions are in reality formed 

 by the circular muscular coat ; which gives off 

 projections or incomplete septa, that compli- 

 cate the general cavity of the tube, by adding 

 a number of supplementary cells. These cells 

 are arranged in three vertical rows ; which are 

 separated by ridges, that correspond to the 

 external depressions formed by the longitu- 

 dinal bands above mentioned. Between these 

 bands, the " haustra" or pouches of the bowel 

 possess a muscular tunic of very inconsider- 

 able thickness : the transverse or circular 

 layer being reduced to a thin membranous 

 lamina ; and the longitudinal being, as before 



stated, altogether absent. The close relation 

 of these longitudinal and transverse septa to 

 the length and width of the bowel is well 

 shown by the effect of cutting across or re- 

 moving its three bands, and then distending the 

 tube by artificial inflation. This obliterates 

 the " falciform folds " or transverse septa ; 

 and thus converts the sacculated intestine 

 into a canal, the length and diameter of which 

 are nearly double of what it formerly pos- 

 sessed when retained in its proper shape by 

 its longitudinal bands or " taeniae." 



The serous covering of the ccecum is chiefly 

 remarkable from the closeness with which it 

 generally attaches the bowel to the fascia over 

 the iliacus muscle. When the tube is but 

 moderately distended, it covers only its ante- 

 rior surface. Extreme contraction can, how- 

 ever, render it a more complete covering; and 

 may even produce it into a kind of meso- 

 caecum behind the bowel. While conversely, 

 great distention of the tube reduces the peri- 

 toneum to a partial investment ; which occu- 

 pies but a third, or even less, of the intestinal 

 surface. 



The mucous membrane of the coecum differs 

 in no essential respect from that of the re- 

 mainder of the large intestine, the structure 

 of which is continued up to the very edge of 

 the valve which severs it from the ileum. 



The caecum has three apertures: one, a 

 large opening by which its cavity is directly 

 continuous with the colon ; a second, which 

 communicates with the small intestine, and is 

 guarded by a double valve ; and a third, which 

 opens into the slender vermiform appendix. 



lleo-ccBcal valve. The opening into the 

 ileum is situated at the upper border of the 

 coecum ; on its left side, and a little poste- 

 riorly. The structures which bound and define 

 this opening are collectively termed the ileo- 

 ccecal or the ileo-colic valve : although these 

 names ought in strictness to be limited to 

 those separate portions of the entire intestinal 

 valve which their etymology would indicate. 



The arrangement of the intestinal tunics 

 in this valve is best seen by inflating and dry- 

 ing that part of the intestine, which includes, 

 together with the last inch or two of ileum, the 

 caecum, and the commencement of the colon. 

 On cutting out a piece of such a dried prepara- 

 tion, so as to gam a view of its interior, we 

 see the valve as represented in the accom- 

 panying figure (Jig. 275.) The small in- 

 testine, generally inclining slightly upwards as 

 well as backwards, passes towards the caecum, 

 at what is thus a rather acute angle. In- 

 stead, however, of opening into the bottom of 

 one of the sacculi of the caecum, it selects for 

 its entry the exact site of the deepest and 

 most projecting of those transverse constric- 

 tions which project into the cavity of the large 

 intestine. This constriction occupies the 

 inner side of the bowel ; and is, as it were, 

 split up by the entering ileum into two laminae ; 

 an upper and a lower, an ileo-colic and an 

 ileo-caecal (e,f,fig. 275.) While, at the same 

 time, the hitherto cylindrical calibre of the 

 small intestine is gradually reduced to a hori- 



