CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 449 



immediate vicinity of the pylorus to the ileocaecal valve, except 

 immediately underneath each villus, and in the spots occupied by 

 the lymphatic follicles of which we shall presently speak. The 

 mucous membrane of the small intestine is in fact to a very large 

 extent made up of a number of these short tubular glands placed 

 side by side and packed closely together, though not so closely as 

 the somewhat similarly arranged cardiac glands of the stomach ; 

 these glands form the greater part of the thickness of the intes- 

 tinal mucous membrane, and the muscularis mucosa? runs in a 

 fairly even line at some little distance below them, that is outside 

 their blind ends. Each gland is a straight or nearly straight tube, 

 rarely dividing, about 400 //, long and 70 //- broad. The outline is 

 furnished by a very distinct basement membrane, in which nuclei 

 are imbedded at intervals, and this basement membrane is lined 

 with a single layer of short cubical cells, leaving a small but distinct 

 lumen ; the cells should perhaps be rather described as somewhat 

 conical, with a broader base at the basement membrane and a 

 narrower apex abutting on the lumen. The cell-body, surrounding 

 a somewhat spherical nucleus, is faintly granular except for a hyaline 

 free border, which however is not so conspicuous or so constant as 

 in the columnar cells of the villi. Similar cells cover the ridges 

 intervening between adjacent glands, and where a villus comes 

 next to a gland the short cubical cells of the gland may be traced 

 into the columnar cells of the villus, the hyaline border becoming 

 more marked and the nucleus becoming oval. Among the cubical 

 cells of the gland are to be found, in varying numbers, goblet cells 

 quite similar to those of the villi. It sometimes happens that 

 during the preparation of a specimen the whole epithelium is 

 shed en 'masse, the cells being much more adherent to each other 

 than to the basement membrane; in such a case the features of 

 the basement membrane are well seen. 



Outside the basement membrane, between adjacent glands and 

 between the blind ends of the glands and the underlying muscu- 

 laris mucosse, is reticular connective-tissue, finer and more truly 

 reticular than that of the villi ; it is perhaps less crowded with 

 leucocytes. In this reticular tissue run, encircling the glands, 

 capillary blood vessels supplied by small arteries coming from 

 the submucous tissue, and pouring their blood into corre- 

 sponding veins, and with this reticular tissue lymphatics are con- 

 nected. 



These glands of Lieberklihn are supposed to furnish the succus 

 entericus. The reasons for this view lie in their tubular form, 



which is that of many secreting glands, in their lumen being too 

 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 



F. 29 



