240 



DIGESTION. 



FIG. 73. 



Valvulce Conniventes. 



The valvulse conniventes commence in the duodenum, 

 about one or two inches beyond the pylorus, and becoming 

 larger and more numerous immediately beyond the entrance 

 of the bile-duct, continue thickly arranged and well developed 

 throughout the jejunum ; then, gradually diminishing in size 

 and number, they cease near the middle of the ileum. In 

 structure they are formed by a doubling inwards of the mu- 

 cous membrane, the crescentic, nearly circular, folds thus 

 formed being arranged transversely with regard to the axis 

 of the intestine, and each individual fold seldom extending 

 around more than or f of the bowel's circumference. Un- 

 like the rugae in the stomach, they do not disappear on dis- 

 tension. Only an imperfect notion of 

 their natural position and function can 

 be obtained by looking at them after the 

 intestine has been laid open in the usual 

 manner. To understand them aright, 

 a piece of gut should be distended 

 either with air or alcohol, and not 

 opened until the tissues have become 

 hardened. On then making a section, 

 it may be seen that instead of disap- 

 pearing, as the rugae in the stomach 

 would under similar circumstances, they 

 stand out at right angles to the general 

 surface of the mucous membrane (Fig. 

 73). Their functions are probably 

 these: Besides (1) offering a largely 

 increased surface for secretion and ab- 

 sorption, they probably (2) prevent the 

 too rapid passage of the very liquid 

 products of gastric digestion, immedi- 

 ately after their escape from the stom- 



hardeued by alcohol) laid b -. /ON -, .-, . ,. j 



open to show the normal ach > and ( 3 )> b 7 their Projection, and 



position of the vaivuise con- consequent interference with a uni- 



niventes. form and untroubled current of the 



intestinal contents, probably assist in 



the more perfect mingling of the latter with the secretions 

 poured out to act on them. 



Glands of the Small Intestine. The glands are of three prin- 

 cipal kinds, named after their describers, the glands of Lieber- 

 kiihn, of Peyer, and of Brunn. The glands or follicles of 

 I/ieberkilhn are simple tubular depressions of the intestinal 



Piece of small intestine 

 (previously distended and 



