362 



STOMACH AND INTESTINE. 



what resembles that of the cells lining the 

 smaller branches of the straight urinary tubules. 

 Where the smaller tubes converge to form the 

 efferent duct that perforates the mucous 

 membrane, these cells are exchanged for 

 short cylinders, the structure of which rapidly 

 merges into that of the ordinary columnar 

 epithelium of the general intestinal surface. 



As regards the secretion of these racemose 

 glands, we can only state that their ducts 

 contain a structureless mucus, which has an 

 alkaline reaction. 



With such an imperfect knowledge of its na- 

 ture, we can scarcely wonder that the office of 

 this fluid remains unknown to us. Like many 

 other animal matters, it converts starch into 

 sugar. But until the precise rapidity and energy 

 of this change have been established, it is im- 

 possible to determine how far this action is 

 really comparable to that of the saliva. From 

 the close resemblance between the sub-mu- 

 cous glands of the mouth and these of the duo- 

 denum, many have assumed them to prepare 

 a salivary fluid. But, besides that we are 

 not warranted in regarding the secretion of 

 the buccal glands as identical with the saliva 

 (of which it forms but a very small ingredient), 

 a very moderate knowledge of histology 

 might suffice to indicate the danger of inferring 

 the nature of any secretion from the mere 

 arrangement of the structures by which it is 

 furnished. Hence it must remain for the 

 present undecided, whether this mucus is a 

 salivary or pancreatic fluid ; or merely a more 

 concentrated form of intestinal juice, secreted 

 by glands which here reach a higher degree of 

 development than that attained by the short 

 cylindrical tubes of the rest of the bowel. 



Large intestine. The remaining portion of 

 the alimentary canal forms the large intestine 



Fig. 274. 



Large intestine, as seen in situ, in a state of moderate 

 inflation. The anterior wall of the belly, and the 

 small intestine, are supposed to have been removed. 



c, caecum ; a, ascending portion of the colon ; t, 

 transverse portion ; d, descending portion ; s, sig- 

 moid flexure ; r, rectum. 



(c a t d s r^fig. 276.) (intestinum crassum, Lat. ; 

 gros intestm, Fr.; dickes Gedarm, Germ.): a 

 name which alludes to the size that is one of its 

 chief characteristics. Beginning at the termi- 

 nation of the ileum, in the right iliac fossa, it 

 passes upwards to the under surface of the 

 liver. Here it turns at a right angle, and runs 

 horizontally below the stomach, to the left 

 extremity of this organ. By a second bend, 

 it here resumes the vertical direction, and 

 then passes downwards towards the left iliac 

 fossa. In this region it undergoes a remark- 

 able curvature, which has the shape of the 

 italic letter S. From the lower end of this 

 "sigmoid" flexure, it passes obliquely towards 

 the median line ; where it terminates in a 

 straight, short tube, that runs vertically 

 through the pelvis to the outlet of the anus. 

 Hence the entire segment of large intestine has 

 the shape of a horse-shoe; and forms a large 

 bend, which is concave downwards, and passes 

 almost round the confines of the abdomen 

 before ending at the inferior extremity of this 

 cavity. While its general arrangement is 

 such, that the intestinal canal, which diverges 

 from the median line at the lower end of 

 the oesophagus, returns to it shortly before 

 terminating in the posterior or lower segment 

 of the trunk. 



An accurate measurement of the length and 

 width of this tube is opposed by the diffi- 

 culties already alluded to in the case of the 

 small intestine. My own observations would 

 indicate an average length of from four to six 

 feet, and a mean diameter of about If to 2^ 

 inches: the two measurements usually vary- 

 ing inversely to each other, except in the cases 

 of extreme distention or contraction, when 

 both respectively increase or decrease simul- 

 taneously. Hence the large intestine has 

 about a quarter the length, and twice the 

 width, of the small. From such an estimate 

 we may conclude that, while its capacity is 

 almost equal to that of the narrower tube, 

 its active surface is scarcely half as large. 

 And even this great difference is much in- 

 creased by the absence of villi and valvuloe 

 conniventes from the interior of the large in- 

 testine. 



Like the rest of the canal, the wall of the 

 large intestine is composed of the serous, mus- 

 cular, and mucous coats; and of vessels, nerves, 

 and lymphatics, which are distributed to them. 



The nature and arrangement of these 

 tunics vary, however, in the several parts of 

 the tube. And these differences, aided by 

 others which affect its size, shape, and situa- 

 tion, subdivide the large intestine into the 

 following segments : the ccecum ; the vermi- 

 form appendix; the colon, in which we dis- 

 tinguish an ascending, transverse, and descend- 

 ing portion, and a sigmoid flexure ; and, finally, 

 the rectum. The anatomy of each of these 

 will demand a brief notice. 



The ccecum (c,Jigs. 276, 277.) (formerly blind 

 gut, Eng.; blind Darm, Germ.) is the first and 

 largest of these segments. Its arrangement may 

 be described as due to the fact, that the small 

 intestine, instead of being simply continuous 



