362 THE SMALL INTESTINE. 



part by a single vein, 'which in man commences near the tip of tho 

 villus, and passes through the mucous membrane into the submucosa 

 witliout receiving lateral twigs.* 



The lacteal lies in the centre of the villus (figs. 256, 257), and is in 

 the smaller villi usually a single vessel, with a closed and somewhat 

 expanded extremity, and of considerably larger diameter than the 

 capillaries of the blood-vessels around. According to the observations 

 of Teichmann, there are never more than two intercommunicating 

 lacteals in a single villus in the human subject ; but both he and Frey 

 found a copious network in the villi of the sheep. Like the lymphatics 

 elsewhere, the lacteals in the villi are bounded by a delicate layer of 

 flattened epithelioid cells. These are connected with the branched cells 

 of the retiform tissue, and these again with the flattened cells which 

 form the basement membrane ; from the latter, prolongations extend 

 between the epithelium cells towards the surface. 



Fis. 258. 



-Efithelium op the Intestinal Villus of a Rabbit (from Kiilliker). 

 A, =-f° ; B, -'l" 



A, series of the columnar epitlielial cells separated from a villus ; a cuticular mem- 

 brane or border is seen passing over the free ends of the cells. 



B, some of the same cells showing the striation of the border. 



The columnar epithelium cells (fig. 258), which cover not only the 

 villi but also the rest of the surface of the intestine, and extend into the 

 tubular glands (fig. 259) are granular in appearance; each with a clear 

 oval nucleus and a tapering extremity next the basement membrane. 

 At the free or superficial end they present a distinct layer of highly 

 refracting substance with vertical strite running through it. This layer 

 was first recognised by Kolliker and by Funke, who both considered 

 the strijB to represent minute perforating canals ; while Brettauer and 

 Steinach, and likewise Henle, maintained them to be solid rods. The 

 cells for the most part contain mucus, which swells up on the addition 

 of water, transforming them into goblet-cells (see p. 211). 



There has been considerable question as to the manner in which fatty 

 matters, which are of course indiff'usible through the moist animal 

 membranes, find their way from the interior of the gut into the com- 

 mencement of the lacteals. It was formerly believed that the minute 

 fatty globules were conveyed into the interior of the villus by the 

 medium of the columnar epithelium cells of the surface, and in accord- 

 ance with this V)oth Kolliker and Bonders have described minute par- 

 ticles of oil as passing through the striated base of the cells. More- 

 over, during digestion, the epithelial cells become turbid with 

 minute oil-droplets in their interior ; and at a subsequent stage the 

 tissue of the villus generally appears pervaded wiih similar fatty par- 



* The general arrangement of the vascular supply of the villi varies considerably in 

 different animals. 



