312 DIGESTION. 



The valvulge conniventes, simple transverse duplicatures 

 of the mucous membrane of the intestine, are particularly 

 well marked in man, though they are found in some of the 

 inferior animals belonging to the class of mammals, as the 

 elephant and the camel. 1 They render the extent of the 

 mucous membrane much greater than that of the other coats 

 of the intestine. Commencing at about the middle of the 

 duodenum, they extend, with no diminution in number, 

 throughout the jejunum. In the ileum they become more 

 and more rare, until they are lost at about its lower third. 

 Sappey found about six hundred of these folds in the first 

 half of the small intestine, and from two hundred to two 

 hundred and fifty in the lower half. He estimates that in 

 those portions of intestine where they are most abundant, 

 they increase the length of the mucous membrane to about 

 double that of the tube itself ; but in the ileum they do not 

 increase the length more than one-sixth. 2 The folds are 

 always transverse and occupy usually from one-third to one- 

 half of the circumference of the tube, though a few may ex- 

 tend entirely around it. The greatest width of each fold is 

 in the centre, where it measures from a quarter to half an 

 inch. From this the width gradually diminishes until the 

 folds are lost in the membrane as it is attached to the mus- 

 cular coat. Between the folds are found fibres of connective 

 tissue similar to that which attaches the membrane through- 

 out the whole of the alimentary tract. This, though loose, 

 is constant, and prevents the folds from being effaced, even 

 when the intestine is distended to its utmost. Between the 

 folds are also found vessels, nerves, and lymphatics. 



The position and arrangement of the valvulae conniventes 

 is such that they move freely in both directions, and may be 

 applied to the inner surface of the intestine either above or 

 below their line of attachment. It is evident that the food, 



1 MILNE-EDWAKDS, Lemons sur la Physiologie ct I 1 Anatomic Comparee, Paris, 

 1860, tome vi., p. 393. 



2 SAPPEY, Traite d 1 Anatomic Descriptive, Paris, 1857, tome iii., pp. 134, 135. 



