PHYSIOLOGICAL ANATOMY OF THE SMALL INTESTINE. 235 



tubules, or follicles of Lieberkuhn ; 4, intestinal villi ; 5, solitary glands, or 

 follicles ; 6, agminated glands, or patches of Peyer. 



The valvulse conniventes, simple transverse duplicatures of the mucous 

 membrane of the intestine, are particularly well marked in man, although 

 they are found in some of the inferior animals belonging to the class of mam- 

 mals, 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. Be- 

 ginning at about the middle of the duodenum, they extend, with no diminu- 

 tion 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 (Sappey). 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. The folds are 

 always transverse and occupy usually one-third to one-half of the circumfer- 

 ence of the tube, although a few may extend entirely around it. The great- 

 est width of each fold is at its centre, where it measures a quarter to half an 

 inch (6'4 to 12'7 mm.). 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 whole of 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 blood-vessels, nerves and lymphatics. 



The position and arrangement of the valvulae conniventes are such that 

 they move freely in both directions and may be applied to the inner surface 

 of the intestine either above or 

 below their lines of attachment. 

 It is evident that the food, as it 

 passes along in obedience to the 

 peristaltic movements, must, by 

 insinuating itself beneath the 

 folds and passing over them, be 

 exposed to a greater extent of 

 mucous membrane than if these 

 valves did not exist. This is 

 about the only definite use that 

 can be assigned to them. 



Thickly set beneath the mu- 

 cous membrane in the first half 



Of the duodenum, and Scattered FlG - & --Gland of Brunner, from the human subject 



here and there throughout the 



rest of its extent, are the duodenal racemose glands, or the glands of Brun- 

 ner. These are not found in other parts of the intestinal canal. In their 

 structure they closely resemble the racemose glands of the oesophagus. On 



