PHYSIOLOGICAL ANATOMY OF THE SMALL INTESTINE. 239 



borders. This vessel is probably in the form of a single tube, either simple 

 or presenting a few short, rounded diverticula. 



The stomata of the lacteal vessel are thought to communicate with 

 lymph-spaces or canals in the substance of the villus. Owing to the ex- 

 cessive tenuity of the walls of the lacteals in the villi, it has been found 

 impossible to fill these vessels with an artificial injection, although the 

 lymphatics subjacent to them may be easily distended and studied in this 

 way. 



No satisfactory account has ever been given of nerves in the intestinal 

 villi. If any exist in these structures, they probably are derived from the 

 sympathetic system. 



The solitary glands, or follicles, and the patches of Peyer, or agminated 

 glands, have one and the same structure, the only difference being that those 

 called solitary are scattered singly in very variable numbers throughout the 

 small and large intestine, while the agminated glands consist of these folli- 

 cles collected into patches of different sizes. These patches are generally 

 found in the ileum. The number of the solitary glands is very variable, and 

 they are sometimes absent. The patches of Peyer are always situated in 

 that portion of the intestine opposite the attachment of the mesentery. 

 They are likewise variable in number and are irregular in size. They usu- 

 ally are irregularly oval in form, and measure half an inch to an inch and 

 a half (12-7 to 38'1 mm.), in length by three-fourths of an inch (19-1 mm.) 

 in breadth. Sometimes they are three to four inches (7*6 to 10-1 centi- 

 metres) long, but the largest are always found in the lower part of the 

 ileum. Their number is about twenty, and they are generally confined to 

 the ileum ; but when they are very abundant for they sometimes exist to 

 the number of sixty or eighty they may be found in the jejunum or even 

 in the duodenum. 



Two varieties of the patches of Peyer have been described by anatomists. 

 In one of these varieties, the patch is quite prominent, its surface being 

 slightly raised above the general mucous surface ; in the other, the surface is 

 smooth, and the patch is distinguished at first with some difficulty. The 

 more prominent patches are covered with mucous membrane arranged in 

 folds something like the convolutions on the surface of the brain. The 

 valvulae conniventes cease at or very near their borders. These are the only 

 patches which are generally described as the glands of Peyer, the others, 

 which may be called the smooth patches, being frequently overlooked. The 

 latter are covered with a smooth, thin, and closely adherent mucous mem- 

 brane. Their follicles are small and abundant. The borders of these patches 

 are much less strongly marked than in those of the first variety. As they are 

 evident only upon close examination and as they are the only patches present 

 in certain individuals, it is said that sometimes the patches of Peyer are 

 wanting. They are usually in less number than the first variety. 



The villi are very large and prominent on the mucous membrane cover- 

 ing the first variety of Peyer's patches, especially at the summit of the folds. 

 In the second variety the villi are the same as over other parts of the mu- 



