THE DIGESTIVE TRACT. 



FIG. 206. 



Goblet-cells are numerous, many epithelial elements having be- 

 come distended with mucoid secretion : in carmine preparations the 

 cells appear as clear, oval breaks in the 

 contour of the epithelium. While occur- 

 ring throughout the entire digestive tube, 

 the goblet-cells are especially numerous in 

 the large intestine, where not infrequently 

 the majority of the epithelial elements are 

 in this condition. During certain stages of 

 digestion the protoplasm of the epithelium 

 may contain oil-drops taken up from the 

 intestinal contents. Migratory leuco- 

 cytes are also found in the intercellular 

 clefts. The epithelium rests upon a mem- 

 brana propria the endothelium of Debove 

 composed of flattened connective-tissue 

 plates. 



The villi consist entirely of the tissues 

 of the mucosa, the epithelium extending 

 over the projecting portions of the tunica 

 propria to form a complete investment of 

 the finger-like processes. The centre of 

 I each villus is occupied by the absorbent 

 )(\ chyle-vessel, or lacteal, a slightly club- 

 shaped lymphatic radicle, which ends 

 blindly near the apex of the villus and 

 whose walls are composed of a single layer 



of endothelium. The tissue surrounding the lacteal and forming 

 the bulk of the projection approaches in 

 character quite closely adenoid tissue, con- 

 sisting of a fibrous reticulum holding many 

 lymphoid cells within its meshes. The 

 central lacteal lies enclosed within a capil- 

 lary net-work, extending through the 

 greater part of the villus and connecting the 

 afferent arteriole and efferent veins. Imme- 

 diately surrounding the lacteal, and in inti- 

 mate relation with it, numerous delicate 

 vertical bundles of non-striped muscle, 

 derived from the underlying muscularis 

 mucosae, ascend towards the tip of the villus. 



The components of the villus are held together by the common 

 adenoid tissue, in whose interstices lie many lymphoid cells and, 

 during certain stages of digestion, numberless fatty granules. At 



g 1 



Simple tubular glands of large 

 intestine of dog: the epithelial 

 elements lining the follicles have 

 become very largely converted 

 into goblet-cells. 



FIG. 207. 



Transverse section of follicles 

 of large intestine of dog : the 

 individual tubules are separated 

 by the fibrous stroma of the 

 mucosa. 



