208 INTESTINAL DIGESTION 



fifths, the lower three-fifths being called the ileum. It has received the 

 name jejunum from the fact that it is almost always found empty after 

 death. 



The ileum is somewhat narrower and thinner than the jejunum, 

 otherwise possessing no marked peculiarities except in its mucous 

 membrane. This division of the intestine opens into the colon. 



Mucous Membrane of the Small Intestine. The mucous coat of the 

 small intestine is somewhat thinner than the lining membrane of the 

 stomach. It is thickest in the duodenum and gradually becomes 

 thinner toward the ileum. It is highly vascular, presenting, like the 

 mucous membrane of the stomach, a great increase in the quantity of 

 blood during digestion. It has a peculiar soft and yelvety appearance, 

 and during digestion is of a vivid red color, being pale pink during the 

 intervals. It presents for anatomical description the following parts : 

 I, folds of the membrane, called valvulae conniventes ; 2, duodenal 

 racemose glands, or glands of Brunner ; 3, intestinal tubules, or folli- 

 cles of Lieberkiihn ; 4, intestinal villi ; 5, solitary glands or follicles ; 

 6, agminated glands, or patches of Peyer. 



The valvulae conniventes, simple transverse duplicatures of the 

 mucous membrane, are particularly well marked in man, although they 

 are founcl in some of the inferior animals belonging to the class of 

 mammals, as the elephant and the camel. They render the extent of 

 the mucous membrane much greater than that of the other coats of the 

 intestine. Beginning at about the middle of the duodenum, they extend, 

 with no diminution in number, throughout the jejunum. In the ileum 

 they progressively diminish in number until they are lost at about its 

 lower third. There are about six hundred of these folds in the first 

 half of the small intestine and two hundred to two hundred and fifty 

 in the lower half. 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. 

 The folds are always transverse and occupy usually one-third to one- 

 half of the circumference of the tube, although a few may extend 

 entirely around it. The greatest width of each fold is at its centre, 

 where it measures a quarter to half an inch (6.4 to 12.7 millimeters). 

 From this point the width gradually diminishes until the folds are lost 

 in the membrane as it is attached to the muscular coat. Between the 

 folds are found fibres of connective tissue similar to those which attach 

 the membrane throughout the alimentary tract. This, though loose, is 

 constant, and it prevents the folds from being effaced, even when the 

 intestine is distended to its utmost. Between the folds are also found 

 bloodvessels, nerves and lymphatics. 



