CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 475 



narrow for the passage of food into it, and in the fact that, as we 

 shall see, they unlike the columnar cells of the villi are not 

 concerned in the absorption of fat ; otherwise there are no definite 

 facts to prove that the cubical cells are concerned in secretion only 

 or that they may not absorb matter other than fat. The goblet 

 cells in these glands as in the villi certainly secrete mucus, and may 

 secrete also some of the constituents of the succus entericus. 



Besides these glands properly so called, that is to say involu- 

 tions of the epithelial (hypoblastic) mucous membrane, there are 

 found in the mucous membrane bodies belonging to the lymphatic 

 system also often called glands, viz. the solitary glands and the 

 agminated glands or patches of Peyer. We shall speak of these as 

 lymphatic follicles, and it will be convenient to study them 

 separately in connection with the lymphatic system. 



264. Immediately below the pylorus in man, but varying 

 somewhat in position in different animals, are the glands of 

 Brunner. These may be regarded as modifications of the pyloric 

 glands of the stomach. In each gland a duct, lined with short 

 columnar epithelium cells leaving a distinct lumen, extends single 

 for some distance, and piercing the muscularis mucosse divides in 

 the submucous tissue into a number of tubes, which subdividing 

 take a twisted course and end in slight enlargements or alveoli. 

 The cells lining both the branching tubes and the alveoli are 

 short cubical cells with an indistinct outline, similar to but, in a 

 fresh condition, more distinctly granular than the cells of the 

 gastric pyloric glands. Bundles of plain muscular fibres, stragglers 

 from the muscularis mucosas, are scattered among the tubes. 



These glands of Brunner when traced back to the stomach are 

 found to pass gradually into the pyloric glands ; traced along the 

 intestine they soon disappear; the ducts of those glands which 

 reach into the duodenum so far as to be found in company with 

 the glands of Lieberktihn and villi, open into the lumina of the 

 former. 



It is not clear that any special purpose is served by these 

 glands of Brunner ; an extract of the glands is said to digest fibrin 

 in the presence of acid. 



The Large Intestine. 



265. The general plan of structure of the large intestine is 

 the same as that of the small intestine, the salient points of 

 distinction being the absence of villi, and, in man, a peculiar 

 arrangement of the longitudinal coat. 



Instead of being uniformly distributed as a thin layer over the 

 whole circumference of the tube as in the small intestine, the 

 longitudinal coat is in the large intestine chiefly gathered up into 

 three thickened bands or bundles, being very thin elsewhere. 



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