228 



DIGESTION. 



XXV. 



the same elements exist in both, basement membrane, epithelium, 

 sub-basement tissue, which occupies, along with vessels and perhaps 



nerves, the interior of the 

 villus. The difference be- 

 tween the two structures 

 is that the epithelium is 

 in the interior of the fol- 

 licle and on the exterior 

 of the villus. 



A single layer of the co- 

 lumnar epithelium covers 

 each villus (fig. 159). 

 The particles adhere by 

 their sharp extremities to 

 the basement membrane, 

 and their bases, packed 

 together present on the 

 surface an appearance of 

 a pavement. 



^ asement 



A. Villi of duodenum of dog, two hours after death, showing 



the substance of the villus retracted from the epithelial invest- bran P i<? rparlll V SPPn 



ment, like a finger from a glove. The process of digestion was ' eadliyst 



not going on at the time of the dog's death, as there was no fhp PTlithplial laVPr falls 



food in the stomach nor chyle in the lacteals. Magnified 80 * 



diameters. ^.fP whlph it is ai)t to do 



B. From the same part, and same dog, showing the epithe- * 



fieT8niamete?s teingattachedandfreeatintervals ' Magni ~ during the digestive pro- 

 cess (fig. 160). It is a 

 single layer of homoge- 

 neous membrane, beneath 

 which, or in the cavity of 

 the villus, are seen, in 

 i well-injected specimens, 

 the blood-vessels of the 

 villus. 



Each villus is provided 

 with a plexus of capil- 

 laries. A single artery 

 enters its base, and, pass- 



A. From the same part of another dog, fed 2 hours before ing Up its Centre, forth- 

 death, showing the columnar epithelium stripped off, and the -<i v.l rr , ,V4-^ 

 cellular substance of the villus covered merely by basement With DreaKS Up llllO a 

 membrane. Magnified 200 diameters, a. Basement mem- -M i -i r. 

 brane, slightly raised. 6. Cellular substance of the villus, Capillary plCXUS, WhlCll IS 

 disposed somewhat in columns. , i-, _ j._ n f ^^ 



B. From the same part and same dog, showing villus de- Seen at ail points O. 

 nuded of epithelium and the basement membrane raised in a ^f n t , T :n,,c- 

 bulla by the endosmosis of water, in which it was immersed. SUrtaCC OI the VlllUS, im- 

 Magnified 200 diameters, a. Basement membrane. 6. Cel- j- i. i r^ ^^j-l, +!. 



luiar substance of the vilius. mediately beneath the 



A. 



B. 



