1180 



SPLANCHNOLOGY 





Each lip of the valve is formed by a reduplication of the mucous membrane 

 and of the circular muscular fibers of the intestine, the longitudinal fibers and 

 peritoneum being continued uninterruptedly from the small to the large intestine. 



The surfaces of the valve directed toward the ileum are covered with villi, and 

 present the characteristic structure of the mucous membrane of the small intestine; 

 while those turned toward the large intestine are destitute of villi, and marked 

 with the orifices of the numerous tubular glands peculiar to the mucous membrane 

 of the large intestine. These differences in structure continue as far as the free 

 margins of the valve. It is generally maintained that this valve prevents reflux 

 from the cecum into the ileum, but in all probability it acts as a sphincter around 

 the end of the ileum and prevents the contents of the ileum from passing too 

 quickly into the cecum. 



The Colon is divided into four parts: the ascending, transverse, descending, and 

 sigmoid. 



Upper segment 

 of colic valve 



Opening of ileum 



Lower segment 

 qf colic valve 



Probe in vermiform 

 process 



FIG. 1075. Interior of the cecum and lower end of ascending colon, showing colic valve. 



The Ascending Colon (colon ascendens) is smaller in caliber than the cecum, with 

 which it is continuous. It passes upward, from its commencement at the cecum, 

 opposite the colic valve, to the under surface of the right lobe of the liver, on the 

 right of the gall-bladder, where it is lodged in a shallow depression, the colic impres- 

 sion; here it bends abruptly forward and to the left, forming the right colic (hepatic) 

 flexure (Fig. 1056) . It is retained in contact with the posterior wall of the abdomen 

 by the peritoneum, which covers its anterior surface and sides, its posterior surface 

 being connected by loose areolar tissue with the Iliacus, Quadratus lumborum, 

 aponeurotic origin of Transversus abdominis, and with the front of the lower and 

 lateral part of the right kidney. Sometimes the peritoneum completely invests 

 it, and forms a distinct but narrow mesocolon. 1 It is in relation, in front, with the 

 convolutions of the ileum and the abdominal parietes. 



The Transverse Colon (colon transversum) the longest and most movable part of 

 the colon, passes with a downward convexity from the right hypochondriac region 

 across the abdomen, opposite the confines of the epigastric and umbilical zones, 

 into the left hypochondriac region, where it curves sharply on itself beneath the 

 lower end of the spleen, forming the left colic (splenic} flexure. In its course it 

 describes an arch, the concavity of which is directed backward and a little upward; 

 toward its splenic end there is often an abrupt U-shaped curve which may descend 



1 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 corre- 

 sponding 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. 



