SMALL INTESTINE 



26l 



formerly known as Kerkring's valvula conniventes), which are seen con- 

 spicuously on opening the intestine. They are thin leaf -like membranes, 

 in places very close together, which, as their name implies, tend to encircle 

 the tube. Sometimes they form short spirals, and they may branch and 

 connect with one another. They begin in the duodenum, and beyond the 

 duodenal papilla they are tall and close together. They are highly 

 developed in the jejunum and form its most characteristic feature. In 

 the ileum they are lower and further apart; and they may come to an 

 end two feet above the colon. The villi correspondingly are taller and 



Villi. 



X X 



Epithelium. 



Plica circularis. 



Intestinal glands 



Submucosa 



Circular muscle. 



FIG. 254. VERTICAL LONGITUDINAL SECTION OF THE JEJUNUM OF AN ADULT MAN. X 16. 

 The plica circularis on the right supports two small solitary nodules, which do not extend into the sub- 

 mucosa; one of them exhibits a germinal center, x. The epithelium is slightly loosened from the 

 connective tissue core of many of the villi, so that a clear space, xx, exists between the two. The 

 isolated bodies lying near the villi (more numerous to the left of the plicaj circulares) are sections of 

 villi that were bent, so that their ends were cut off in sectioning. 



more numerous in the jejunum than in the ileum, in the distal part of which 

 they are short and scattered, finally disappearing on the colic surface of 

 the valve of the colon (ileo-csecal valve). Thus few and short villi and 

 scattered plicae indicate that a section of the intestine is from the ileum. 

 As seen in sections, the plica circulares are elevations of the sub- 

 mucosa (Fig. 254) covered on both sides by the entire mucous membrane 

 villi, glands and the muscularis mucosae. A low plica of the duodenum 

 is shown in Fig. 251. 



