THE ALIMENTARY CANAL 



3G9 



The villus is formed by a projection of the corium which is cov- 

 ered by the lining epithelium of the intestine. The axis of the villus 

 contains a large lymphatic capillary or lacteal, which begins in the 

 inner third and proceeds outward through the corium to enter a lym- 

 phatic plexus lying just within the muscularis mucosa3. An occasional 

 villus may contain several lacteals. In the base or outer portion of 

 the villus the lacteal is surrounded by small groups of smooth muscle 

 fibers which are disposed in an axial 

 direction, and which are ontogenet- 

 ically derived from the muscularis mu- 

 cosae. Many of these fibers turn out- 

 ward and are attached to the basement 

 membrane beneath the epithelium at 

 the sides and tip of the villus. By 

 their rhythmic contraction the muscle 

 fibers of the villus aid in expelling the 

 contents of the lacteal. 



The body of the villus consists of 

 diffuse lymphoid tissue having a reticu- 

 lar stroma in which the lacteal, the 

 muscle fibers, and the blood-vessels are 

 embedded. 



Each villus is supplied with one or 

 more arterioles which enter at the base 

 and pass to the inner third, where they 

 form an abundant capillary plexus 



about the blind extremity of the lacteal and in the apex of the villus. 

 Minute venules collect the blood from this plexus, and following the 

 course of the lacteal, make their exit from the base of the villus to join 

 the venous plexus in the deeper part of the mueosa (Fig. 347). 



The Lining Epithelium. The lining epithelium of the intestine, 

 which also clothes the villi, rests upon a distinct reticular basement 

 membrane and consists of columnar and goblet cells. The large num- 

 ber and peculiar appearance of the goblet cells is highly characteristic 

 of this tissue. 



The columnar cells are peculiar in that they possess a characteristic 

 striated cuticular border when examined under moderately high magni- 

 fication. They possess a finely reticulated cytoplasm and an ovoid 

 nucleus which is situated at the proximal end or base of the cell. Fre- 

 quently the cytoplasm contains droplets of fat which are in process 



FIG. 344. LONGITUDINAL SECTION 

 OF VILLUS. 



G, goblet cell; L, lacteal; s, stri- 

 ated border of columnar cell. 



