314 DIGESTION. 



most important glandular structures in the intestinal cavity } 

 are found throughout the whole of the small and large intes- 

 tine. In examining a thin section of the mucous membrane, 

 these little tubes are seen closely packed together, occupying 

 nearly the whole of its structure. From the great extent of 

 the membrane, it can readily be conceived that their number 

 must be immense. Between the tubules are blood-vessels 

 embedded in a dense stroma of fibrous tissues with numerous 

 of the unstriped muscular fibres. In a vertical section of the 

 mucous membrane, the only situations where the tubules are 

 not seen are in that portion of the duodenum where the 

 space is occupied by the ducts of the glands of Brunn, and 

 immediately over the centre of the larger solitary glands 

 and some of the closed follicles which are collected to form 

 the patches of Peyer. The tubes are not entirely absent in 

 the patches of Peyer, but are collected in rings, twenty or 

 thirty tubes deep, which surround each of the closed follicles. 

 A microscopical examination of the surface of the mucous 

 membrane by reflected light shows that the openings of the 

 tubules are between the villi. 



In their anatomical characters, the tubules closely resemble 

 the tubes of the stomach, especially those found in the py- 

 loric portion. They are composed externally of a structure- 

 less basement membrane, and are lined with a single layer of 

 columnar epithelium like the cells which cover the villi ; the 

 only difference being that in the tubes the cells are a 

 little shorter. These cells never contain fatty granules, even 

 during the digestion of fat. The central cavity which the 

 cells enclose, which is about one-fourth of the diameter of the 

 tube, is filled with a clear viscid fluid, w T hich is the most im- 

 portant constituent of the intestinal juice. The length of 

 the tubules is equal to the thickness of the mucous membrane, 

 and is about -f-g of an inch. Their diameter is about ^ F of 

 an inch. In man they are cylindrical, terminating in a sin- 

 gle, rounded, blind extremity, which is frequently a little 

 larger than the rest of the tube. These tubules are the chief 



