CHAP. IX.] STRUCTUKE OF THE SMALL INTESTINE. 399 



numerous, smaller, and more irregular in the lower part, the crypts 

 have nearly the same characters and are distributed throughout. 

 Very much as* in the case of the stomach, the muscularis mucosse 

 runs in an even line (except for the sweep of the valvulse conniventes) 

 at a little distance from the bases of the closely packed crypts, and 

 at a greater distance (viz. the length of the crypts) from the bases of 

 the villi ; as we shall see, however, the muscularis mucosse sends up 

 muscular fibres into each villus." 



The crypts of Lieberkiihn are lined by columnar or rather cubical 

 epithelium which is continuous with that which covers the intestinal 

 surface and the villi. 



" They are straight or nearly straight tubes about 400//, long and 

 TOyu, 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 mucous 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...." 



" Outside the basement membrane between adjacent glands and 

 between the blind ends of the glands and the underlying muscularis 

 mucosae, 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 corresponding veins, and with this 

 reticular tissue lymphatics are connected...." 



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

 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 glands of Peyer." 



The glands 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 1 . In each gland a duct, lined with 



short columnar epithelium cells leaving a distinct lumen, extends 



1 Heidenhain, Archiv f. microscop. Anat. Vol. vin. (1872), p. 279. 



