STRUCTURE OF THE SMALL IXTESTIXE. 



527 



valvular conniventes as to give to the membrane its velvety appear- 

 ance. In the duodenum they are broader and less elevated, resem- 

 bling folds and lamina? T ^ to ^ of an inch high, and ^ to even 

 Y 1 ^ of an inch broad. In the jejunum they are mostly conical and 

 flattened, and often cylindrical, clavate, or filiform ; being ^ to ^ 

 of an inch long, ^ to T J^ of an inch, or less, in breadth, and ^\-$ 

 of an inch (in the flattened forms) thick. The epithelium of the 

 villi is the simple conoidal variety. The proper villas itself is sim- 

 ply a solid process of the corium whose matrix is undeveloped col- 

 lagenous tissue, in which a variable number of roundish free nuclei 

 are scattered; containing bloodvessels, lymphatics, and smooth 

 muscular fibres. The bloodvessels are very numerous. Two or 

 three small arteries (ysV^ to 75^ f an inch) give off' a close net- 

 work of capillaries, -joW to 2sW f an i n h i n diameter, which 

 lies immediately beneath the basement membrane on the outer 

 surface of the proper villus itself. From the gradual confluence 

 of these capillaries a vein arises which carries the blood into the 

 larger trunks of the submucous tissue. (Fig. 355.) The lympha- 



Fig. 355. 



Fig. 356. 



Fig. 353. Vertical section of the coats of the small in- 

 testine of a dog, showing only the commencing por- 

 tions of the portal veins, and the capillaries. The 

 injection has been thrown into the portal vein, but 

 has not penetrated to the arteries, a. Vessels of the 

 villi. &. Of Lieberkiihn's tubes, c. Of the muscular 

 coat. 



Fig. 356. Two villi without epithelium, and with the 

 lacteals in their interior (from the calf) ; treated with 

 a dilute solution of caustic soda. (KUlliker.) 



