138 TOPOGRAPHIC AND APPLIED ANATOMY. 



PLATE 18. 



The position of the liver (a portion), duodenum, pancreas, left kidney, and cecum of a fifteen-year-old girl. A 

 deeper layer of the model of Plate 16. 



The relation to the duodenum has been described upon page 134. The long and broad 

 transverse mesocolon should also be borne in mind, since it is responsible for the fact that 

 the transverse colon is much more movable than the ascending or descending ones. The 

 transverse colon is consequently in contact with the anterior abdominal wall, and, if its 

 mesocolon is long enough, may form a loop the convexity of which is directed downward. [At 

 either end the mesentery of the transverse colon becomes shorter, approaching the arrangement of 

 the ascending and descending colons, which are usually without any mesentery. ED.] 



The descending colon (Plates 11-17) is longer than the ascending colon and commences at 

 the left kidney. It runs downward upon the quadratus lumborum muscle, somewhat further 

 from the median line than the ascending colon, reaches the left iliac fossa, and, after a short 

 course toward the middle line, becomes continuous with the sigmoid colon (omega loop) at the 

 external iliac vessels. The attachment to the posterior abdominal wall is similar to that of the 

 ascending colon. Since the broad posterior surfaces of the ascending and descending portions 

 of the large intestine are attached to the posterior abdominal wall by connective tissue, it is pos- 

 sible to open these portions of the intestine from behind without entering the abdominal cavity. 

 This is done in the operation of lumbar colotomy when an artificial anus is made in the descend- 

 ing colon to the outer side of the quadratus lumborum muscle above the left iliac crest. (Find 

 this location in Plate 16.) It should be noted, however, that these portions of the intestine may 

 occasionally have a short mesocolon, the peritoneal reflection being almost complete, in which 

 case the operation is very difficult to perform without opening the peritoneal cavity. The sig- 

 moid colon is the most favorable, and the one generally preferred for the performance of this 

 operation, in a case of rectal carcinoma, for example, where the intestine is occluded above the 

 anus (Plates n and 14-18). It is situated in the right iliac region connecting the descending 

 colon with the rectum, and is distinguished from the former by its long mesocolon. It is usually 

 in contact with the anterior abdominal wall upon the left side above Poupart's ligament, and 

 can be exposed and opened in this situation. This operation is necessarily preceded by a lapar- 

 otomy. In making an artificial anus the opening made in the intestine must be united with the 

 edges of the abdominal incision so that none of the intestinal contents may find their way into 

 the peritoneal cavity. In this operation the small intestine must not be mistaken for the 

 colon. The characteristics of the colon are that its longitudinal muscular coat is arranged 

 into three bands or taenia and that it has epiploic appendages containing fat. This region 

 is depicted in Fig. 57. [Other distinguishing features of the large intestine are: its sacculation, 

 more fixed position, in the case of the more movable divisions, their continuity with the 

 parts relatively fixed, and, as a rule, larger calibre. In addition, the large intestine is more 

 liable to contain hardened feces. It must not be forgotten that the longitudinal bands (taenia 

 coli) above referred to spread out on the lower part of the sigmoid so as to make a covering com- 

 plete except for a narrow strip along either side; that is, the three narrow bands have been 

 reduced to two wider ones, an anterior and a posterior. In the rectum these bands practically 

 disappear. ED.] In cutting from without inward the following structures are divided: skin, 



