STOMACH AND INTESTINE. 



365 



For not only are its shape, size, and direc- 

 tion such as admirably adapt it to this pur- 

 pose, but its development in different species 

 and individuals closely corresponds to the 

 degree in which such a delay is advantageous 

 to digestion. Thus the large caecum of the 

 Herbivora is contrasted, in the Carnivora, by 

 one of but inconsiderable size and development. 

 While there are grounds for conjecturing, that 

 the habitual use of a vegetable diet is capable 

 of increasing its size in the human subject. 

 In all of these respects, however, its develop- 

 ment does but parallel that of the remainder 

 of the large intestine. We may therefore defer 

 considering the nature of its secretion, and 

 the changes undergone by its contents, until 

 these segments of the bowel have also been 

 noticed. 



The vermiform appendix (g,j%. 275.) which 

 is so named from its resemblance in shape and 

 size to a worm, is a small, smooth, cylindrical 

 tube ; that opens into the caecum below (and 

 rather posterior to) the aperture of the small 

 intestine. Its length varies from one to four 

 or five inches : its diameter from about a fourth 

 to a third of an inch. Its attached end of course 

 shares the situation of the contiguous part of 

 the caecum. Its distal extremity is usually 

 free ; and may hence be found in almost any 

 situation which its length, and that of the 

 short mesentery that binds it down, together 

 allow it to take. Its opening into the caecum 

 is often partially occluded by a kind of trans- 

 verse fold or valve. 



As regards its structure, the vermiform ap- 

 pendix exhibits all three of the ordinary coats. 

 Its peritoneum is derived from that of the 

 caecum, and often forms a short fold or me- 

 sentery which is prolonged up a part of its 

 length. Its muscular stratum is of uniform 

 and considerable thickness, and is continuous 

 with the three longitudinal bands which give 

 the ceecum its sacculated shape. Its mucous 

 membrane is occupied by tubes and follicles, 

 like those of the colon. And the latter 

 structures are often present in such extra- 

 ordinary numbers, as to constitute almost 

 a continuous layer of these minute closed 

 sacs. The calibre of the tube, which is in 

 general disproportionately small, is occupied 

 by a sparing quantity of glairy mucus ; and 

 occasionally, by small fragments of the ordi- 

 nary intestinal contents. 



The use of the vermiform appendix is un- 

 known. It has been suggested to be a mere 

 relic of the umbilical duct of the foetus : an 

 erroneous view, to which allusion will hereafter 

 be made in speaking of the development of the 

 intestinal canal. It is almost peculiar to Man ; 

 in whom its situation often causes it to receive 

 small solids in their transit through the caecum, 

 with the result of their becoming impacted in 

 its narrow cavity. This accident is some- 

 times followed by inflammation and perfora- 

 tion of the tube, causing fatal peritonitis. 



The colon* (formerly Great gut, Eng.; 



* This Greek word, which has been adopted into 

 most of the modern languages, is derived indiffe- 



Grimmdarm, Germ.), which forms by far the 

 greater part of the large intestine, extends from 

 the ilio-caecal valve to the rectum. Starting 

 from the right iliac fossa, it passes vertically 

 {a, Jig. 274.) up the posterior wall of the belly, 

 and on the right side of the spine, until it 

 reaches the under surface of the liver. A 

 sudden turn at a right angle marks the end 

 of this ascending portion, and the beginning 

 of its transverse part. The latter segment, 

 though tolerably horizontal, forms an arch 

 (t,fig. 274.) with the convexity forwards, so as 

 to pass around the projecting spine and aorta. 

 Below the spleen it merges, by another rectan- 

 gular bend, into the descending colon (d,jig. 

 274.) This takes much the same course on the 

 left side of the abdomen as the ascending colon 

 does on the right ; and opposite to the crest of 

 the ileum, it ends by becoming continuous 

 with the sigmoid flexure (s,fig. 274.), The 

 latter portion is attached by a short mesen- 

 tery to the left iliac fossa; and it terminates 

 in the rectum, at a point corresponding to the 

 left sacro-iliac symphysis. 



The relations of each of these segments to 

 the adjacent textures and organs may be 

 easily deduced from their course as described 

 above. 



Thus the ascending colon lies on the right 

 kidney and quadratus lumborum muscle, from 

 which it is only separated by loose areolar 

 tissue. On its left side, is the psoas muscle ; 

 and above it, the vertical portion of the duo- 

 denum. In front, it is covered by coils of in- 

 testine ; or, if sufficiently distended to thrust 

 these away, by the anterior wall of the belly. 



The transverse colon is almost always in 

 contact with the omentum and abdominal pa- 

 rietes, which it touches in the horizontal line 

 that marks the mutual limit of the umbilical 

 and epigastric regions. Above it, is the first 

 portion of the duodenum; with the stomach, 

 liver, gall bladder, and spleen. Below it, are 

 the coils of the small intestine. Behind it, lie 

 the second and third portions of the duo- 

 denum, the latter covering the aorta. To its 

 posterior surface is attached the transverse 

 mcso-colon; which connects this part of the in- 

 testine with the wall of the belly, by a double 

 fold of peritoneum, that splits to enclose the 

 tube. The double lamina formed by the re- 

 union of these two layers of serous membrane 

 in front of the bowel, is continuous, at the 

 lower border of the great omentum, with the 

 similar process that descends from the great 

 curvature of the stomach.* 



The descending colon, like the ascending, 

 lies on the left kidney and the left quadratus 

 lumborum muscle, and is covered by a va- 

 riable quantity of the small intestine. 



The sigmoid flexure is much more frequently 

 in contact with the abdominal wall than the 

 preceding portion of the colon. And its 

 freedom of movement, to which this contact 

 is partly due, also allows the bowel to deviate 

 considerably from its ordinary curvature and 



rent! y from **, membrum, and ***, atvus (T$ TV* 



See Art. PERITONEUM. 



