486 ABDOMEN 



remainder of the intestine is to tie a ligature around the lower cut end of the 

 ileum, and fill the intestine as full as possible with water. The scissors can 

 now be easily carried along the line of the mesenteric attachment^ and the 

 intestine slit open in its entire length. The intestine can be laid open with 

 much greater ease if a piece of costal cartilage be impaled upon that blade 

 of the scissors which is introduced into the bowel. 



Mucous Membrane of the Small Intestine. The plica circu- 

 lares (Q.l.valvulce conniventes} are the most conspicuous objects 

 on the inner wall of the small intestine. These are folds of 

 the mucous membrane placed more or less transversely to 

 the long axis of the intestine. Note particularly that they are 

 permanent folds, and that no amount of stretching or distension 

 of the walls will cause their obliteration. On careful study 

 of the dried specimen three main varieties of plicae 

 circulares may be recognised. The great majority are in the 

 form of crescentic folds, which extend for a variable distance 

 round the wall of the intestine ; others form complete rings 

 around the interior of the intestine ; whilst the third variety, 

 and usually the least numerous, are arranged in a spiral manner, 

 and take from one to three spiral turns around the wall of the 

 intestine. Each fold consists of two layers of mucous mem- 

 brane, with a little intervening areolar tissue derived from the 

 submucous coat. The other coats of the intestine take no 

 part in the formation of the valvulae conniventes. In the 

 upper part of the jejunum the valvulae conniventes are 

 strongly developed, and placed so closely together that the 

 intervals between them are hardly greater than the thickness 

 of one of the folds. Lower down, however, they gradually 

 diminish in numbers, become more widely separated, more 

 oblique in their direction, and not nearly so prominent. 

 Approaching the middle of the ileum, they become exceed- 

 ingly sparse and far between, and a little beyond this they 

 usually disappear altogether. 



The chief function of the valvulae conniventes is to increase the absorbing; 

 and secreting surface of the small intestine. 



Another peculiarity characteristic of the mucous lining of 

 the small intestine is the presence of villi. These are 

 minute projections of the mucous membrane, varying in 

 length from about the -^j-th to ^th of an inch. They occur 

 in enormous numbers over the entire extent of the inner 

 surface, of the intestine, not only upon the plicae circulares, 

 but also in the intervals between them, and they give to the 

 mucous membrane a velvety or fleecy appearance. 



