486 



MANUAL OF HISTOLOGY. 



which ascend at one side, bend over at the apex, and follow the opposite 

 wall in returning, as venous vessels (c). Between these afferent and 



efferent vessels a capillary net- 

 work exists, sometimes exceed- 

 ingly complex, sometimes very 

 simple in its arrangement (&). 

 It not unfrequently happens 

 that a system of capillaries is 

 first given off by the arterial 

 twig to supply the glands of 

 Lieberkulm (d), opening at the 

 base (fig. 474, a to the right) 

 of the villus, which system is 

 simply continuous with that of 

 the latter (b to the right). 



The diameter of the arterial 

 vessel may rise to 0-226-0-0282 

 mm., that of the vein to 0*0451 

 mm. In calibre the capillaries 

 measure on an average 0*0074 

 mm., and their arrangement 

 is usually in elongated meshes. 

 The disposal in loops of the 

 arteries in their transition into 

 veins may be absent, a capillary network being interposed between the 

 two vessels at the summit of the villus. 



We have already alluded (p. 374) to the 

 coecal chyle canal of the intestinal villus. 

 "When the latter is more than usually broad 

 there may be two or even several of these 

 blind tubes, but when small and slender 

 they are only single. The chyle canal occu- 

 pies the axis of the villus, and presents itself, 

 under ordinary treatment (fig. 472, d), in cer- 

 tain cases quite distinctly as a tube formed 

 of a homogeneous non-nucleated membrane, 

 on an average 0*023 mm. in diameter. On 

 treatment with a solution of nitrate of silver, 

 however, this tube is easily shown to be 

 composed of a layer of those jagged-edged 

 vascular cells already so frequently alluded 

 to. It may be seen with great clearness when 

 injected artificially, and also in the villi of 

 animals killed while engaged in digesting an 

 abundance of fatty food (fig. 476). 



Fig. 474. Vascular system of an intestinal villus in the 

 rabbit, a, the arteries (shaded), breaking up first 

 into a capillary network around the glands of Lieber- 

 kiihn (d) ; 6, network of capillaries in the villus; c, 

 venous vessels (unshaded). 



255. 



Turning now to the glandular elements of 

 the small intestine, we shall commence with 

 the least important, namely, with the race- 

 mose mucous glands (fig. 477, &), known com- 

 monly as Brunner's. They are confined to the duodenum, and begin close 

 to the stomach, closely crowded together into a regular adenous layer 



Fig. 475. Vascular network from 

 the intestinal villus of a hare, with 

 its arterial branch 6, capillaries c, 

 and venous branch a. 



