THE INTESTINAL CANAL. 1035 



This valve has been named after nearly all the following men. It was discovered in 1573 

 by Varolius, who called it an opercuJum. Six years later Bauhin called it vahula. Fabricius 

 in 1618 first tried its function by insufflation. Casserius, Tulpius. and Bartholin repeated the 

 experiments. Morgagni in 1719 gave the best description. Window and Albinus followed 

 him. 



Colon. As in the csecum, the outer surface of the colon is prismatic and tri- 

 angular. Four characteristics are observed : 1. Three taenise which start from 

 th^ root of the appendix; 2. Three rows of sacculi between the bands; 3. Con- 

 strictions which separate the sacculi of each row ; 4. Appendices epiploicse. 

 The internal surface has a reverse conformation, the projections between the 

 pouches being called plicce sigmoidece. 



The ascending colon is smaller than the caecum, with which it is continuous, 

 and larger than the transverse colon. It is very short. It passes up through 

 the right lumbar region into the right hypochondrium until it reaches the inferior 

 surface of the right lobe of the liver to the right of the gall-bladder, the impressio 

 colica. It is retained in contact with the posterior abdominal wall by peritoneum 

 which covers its anterior surface and sides, its posterior surface being connected 

 by loose areolar tissue with the fascia covering the Quadratus lumborum and 

 Transversalis muscles, and with the front of the lower and outer part of the right 

 kidney. An abscess of the right kidney could thus break through into the ascend- 

 ing colon and not wound the peritoneum. It is in relation in front with the 

 abdominal wall and convolutions of the ileum. Sometimes the peritoneum nearly 

 surrounds the colon and forms a short mesocolon. 1 On the under surface of the 

 liver in the region of the gall-bladder, the ascending colon forms a sharp angle 

 from the posterior abdominal wall to the front and the left, becomes somewhat 

 superficial, and continues into the transverse colon. This is the hepatic or right 

 colic flexure, bound to the under surface of the liver by the lig. hepato-colicum. 



The transverse colon is the longest part of the large intestine, averaging 

 twenty inches, while the ascending colon is eight inches, and the descending, 

 from the splenic flexure to the crest of the ilium, is eight and a half inches. It 

 passes from the hepatic flexure in the right hypochondrium transversely and 

 slightly upward from right to left along the anterior abdominal wall to the splenic 

 flexure in the left hypochondrium (Fig. 626). Since the colon is longer than 

 the width of the abdomen it describes an arch, transverse arch of the colon, Avith 

 its convexity directed downward and forward. 



It is the most movable part of the colon, for it has a very long mesentery, 

 the transverse mesocolon, which allows it a variable position. Its usual position 

 corresponds to the line separating the umbilical and epigastric regions. In four 

 times out of five it is above the umbilicus. It is in relation by its upper surface 

 with the under surface of the liver and gall-bladder, greater curvature of the 

 stomach and lower end of the spleen ; by its under surface with the small intes- 

 tine ; by its anterior surface with the great omentum and abdominal walls ; by- 

 its posterior surface with the transverse mesocolon ; on the right with the second 

 part of the duodenum, and to the left of this with some convolutions of the 

 small intestine. If this colon has a very direct and obliquely ascending course, 

 the greater curvature of the stomach will be behind its left portion. 



In some cases the transverse colon may present a V- or U-shaped bend de- 

 scending as far as the pubes. These bends are always downward, abrupt, and 

 angular. Treves thinks they are due to habitual distention or to congenital 

 causes (Fig. 656). They are normal in many animals. 



The descending colon is continuous with the transverse by the splenic flexure, 



1 Mr. Treves states that, after a careful examination of one hundred subjects, he found that in 

 fifty-two there was neither an ascending nor a descending mesocolon. In twenty-two there was a 

 descending mesocolon, but no trace of a corresponding fold on the other side. In fourteen subjects 

 there was a mesocolon to both the ascending and the descending segments of the bowel, while in the 

 remaining twelve there was an ascending mesocolon, but no corresponding fold on the left side. It 

 follows, therefore, that in performing lumbar colotomy a mesocolon may be expected upon the left 

 side in 36 per cent, of all cases, and on the right in 26 per cent. (The Anatomy of the Intestinal Canal 

 and Peritoneum in Man, 1885, p. 55.) 



