7?o A MANUAL OF ANATOMY 



bloodvessels, (3) one or more lacteal vessels ensheathed by plain 

 muscular tissue ; and (4) arborisations of nerve-fibrils derived from 

 the plexus of Meissner. 



Between the columnar epithelial cells of the free surface, many of 

 which are mucus-secreting goblet cells, there are amoeboid lymph 

 corpuscles. Beneath the epithelium is a basement membrane 

 composed of flattened cells, and known as the subepithelial endo- 

 thelium. The cells of this basement membrane send processes 

 outwards between the columnar cells of the free surface, and they 

 also send processes inwards which are connected with the branched 

 cells of the retiform tissue of the adenoid tissue. One artery 

 (sometimes two) enters the base of the villus and ascends to near 

 the centre. Here it breaks up into a number of branches, which 

 form a copious capillary network. From this plexus the blood is 

 returned by one or two venous radicles, which leave the villus at 

 its base, where they open into the venous plexus of the mucous 

 membrane. In the centre of the villus there is a lacteal vessel, 

 which commences near the tip in a blind bulbous extremity, or, if 

 there should be two lacteals, they originate in the form of a loop. 

 The wall of the lacteal vessel is formed by a single layer of endo- 

 thelial plates, which are connected by processes with the branched 

 cells of the retiform tissue of the adenoid tissue. The vessel is 

 ensheathed by longitudinal plain muscular fibres derived from the 

 muscularis mucosae, their fibre-cells being connected with the base- 

 ment membrane of the villus. The villus is pervaded by adenoid 

 tissue — that is to say, retiform tissue with its meshes filled with 

 amoeboid lymph corpuscles. The branched cells of this retiform 

 tissue are connected by processes on the one hand with the endo- 

 thelial plates which compose the wall of the lacteal vessel, and on 

 the other hand with the cells of the basement membrane near the 

 surface, and these latter in turn send out processes between the 

 columnar epithelial cells of the free surface. 



The villi play a most important part in absorption, partly through 

 their copious capillary networks, and partly through their lacteals. 

 The lacteals serve specially for the absorption of fats, which is 

 probably effected in the following manner : the columnar epithelial 

 cells at the free surface take up the saponified and emulsified fats, 

 which they transfer to the amoeboid lymph corpuscles between them. 

 These corpuscles then carry the fats inwards through the adenoid 

 tissue into the lacteal vessel. 



Brunner's glands are confined to the duodenum, and are serially 

 continuous with the pyloric glands of the stomach. They are 

 very numerous in the commencement of the duodenum, where 

 they form a continuous layer of gland tissue extending as low 

 as the entrance of the common bile-duct and pancreatic duct. 

 Beyond this point they gradually diminisU in number, and 

 ultimately disappear near the duodeno-jejunal flexure. They 

 belong to the class of racemose or acino-tubular glands, and they 

 differ from the pyloric glands of the stomach in having their tubules 



