968 



THE OEGAXS OF DIGESTIOX 



soon attains its full length, and within one foot of the end of the duodenum is 

 already six inehes in length. 



The ordinary type of mesentery conforms to the figure of half a circle, ))Ut the 

 membrane is lial>ie to considerable variation. It is not unconnnon to find the 

 mesentery maintaining a considerable length up nearly to the end of the ileinn. 



Structure of the small intestine. — Its coats are four in number — viz., serous, 

 muscular, areolar, and mucous. The intestine receives its serous covering from the 

 peritoneum, and, with the exception of certain parts of the duodenum which have 

 l)een described, it is covered entirely by it, save only where the layers leave it 

 behind to form the mesentery. The line of attachment of the mesentery marks 

 the attached border of the small intestine. 



The mu-n-ulnr coat is divided into an external longitudinal layer and an internal 

 circular, the circular being the thicker of the tAvo. Both layers are uniform around 

 the liowel, and l)ecome thinner as the crecum is approached. 



The areolar or submucous coat consists of areolar tissue connecting the muscular 

 and mucous tunics. A thin layer of muscular tissue separates the mucous mem- 

 brane from the areolar coat (muscularis mucosae). 



The mucous coat, thicker at the upper part than the lower part, is lined through- 

 out with colunmar epithelium and is very vascular. The Avhole surface is covered 



Fig. 57:1 



-PORTIOX OF THE SmAI.I. INTESTIXE, LAID OPEX TO SHOW THE 



Valvule Coxniventes. (Biintou.) 



Avith minute jjrocesses called villi ; these give the membrane a finely flocculent 

 apj>earance, which has been compared to the pile of velvet. They are largest and 

 most numerous in the duodenum and jejunum, and become gradually shorter, 

 smaller, and fewer on the ileum. Besides the villi are certain large folds or valvu- 

 lar flaps: these are the valvule conniventes. They are permanent crescentic folds of 

 mucous membrane set transversely to the long axis of the intestine. The majority 

 extend from one-half to two-thirds of the distance round the lumen (tig. 573). The 

 largest are more than two inches long, and al)out one-third of an inch wide. Some 

 of the valvula? conniventes form complete circles and others spirals. These mucous 

 folds do not exist at the beginning of the duodenum. They are very large just 

 Ix'low the entrance of the Inle-duct, and remain conspicuous until the middle of the 

 jejunum is reached. They then become smaller, and gradually disa])pear at the 

 lower part of the ileum. 



Scattered over the whole of the mucous membrane of the small intestine are 

 numerous minute soft rounded bodies composed of retiform tissue. These are the 

 so-called solitary glands. 



Certain patches, called reijer\s patches, are found in the lower ileum. They are 

 oval, are from one-half to three inches in length, and about one inch in breadth, 

 and are placed in the long axis of the bowel along a line most remote from the 

 mesentery. They are made up of an aggregation of solitarv glands. 



