VALYULiE COXNIVENTES. 



359 



it is placed. By turning a portion of the intestine inside out, and then 

 blowing forcibly into the cavity, the areolar tunic may be inflated, the 

 air being driven into its areolar tissue through the part at which 



Fig. 253. — Diagrammatic View in Pkrspkctive 

 OF A Portion of the Coats of the Stomach 

 AND Duodenum, includino the Pylorus 

 (Allen Thomson). 



g, inner surface of the gastric mucous mem- 

 brane ; //', section of the mucous membi-ane with 

 the pyloric gastric glands ; r, the villous surface 

 of the raucous membrane of the duodenum ; i, 

 section of the same with the intestinal glands or 

 crypts of Lieberkiihn ; pp, the ridge of the 

 pyloric ring, with a section of its comi)onent 

 parts ; vii, deep or circular layer of muscular 

 tibixs : these are seen in the section to form 

 the pyloric sphincter ; mc, external or longi- 

 tudinal layer of muscular fibres ; », the serous 

 covering. 



Fig. 253. 



■'•'fUiiummni'"' ' 



the peritoneal investment is wanting. It supports the mucous mem- 

 brane, and forms a layer of loose substance in which the vessels divide 

 and subdivide into smaller branches, preparatory to entering that mem- 

 brane. It consists of areolar tissue, mixed with fine elastic fibres. 



The internal coat or mucous membrane, is characterised by present- 

 ing all over its inner surface a finely flocculent or shaggy appearance, 

 like the pile upon velvet, owing to its being thickly covered with 

 minute processes, named villi; hence it is also named the villous coat. 

 It is one of the most vascular membranes in the whole body, and is 

 naturally of a reddish colour in the upper part of the small intestine, 

 but becomes paler, and at the same time thinner, towards the lower end. 

 It is covered like that of the stomach with a columnar epithelium 

 throughout its whole extent, and next to the submucous coat is bounded 

 by a layer of plain muscular 



tissue {muscular is mucos(e) ; Fig. 254. 



between this and the epithe- 

 lium the substance of the mem- 

 brane, a])art from the tubular 

 glands which will be afterwards 

 described, consists mainly of 

 retiform tissue which supports 

 the blood-vessels and lacteals, 

 and encloses in its meshes 

 numerous lymph-corpuscles. 



The folds and wrinkles found 

 upon the inner surface of the 

 oesophagus and stomach may 

 be completely obliterated by 

 full distension of those parts of the alimentary canal. In the lining 

 membrane of the small intestine, however, there exist besides such 

 effaceable folds, other permanent ones, which cannot be obliterated, even 

 when the tube is forcibly distended. These permanent folds are the 

 valvulsB couniventes, or valves of Kerkring (fig. 254). They are 

 crescentic projections of the mucous membrane, placed transversely to 

 the course of the boweh each of them reachinsc about one-half or two- 



Fig. 



254. — Portion of Small Intestine laid 



OPEN TO SHOW the VALVULiE CoNNIVENTES 



(Briuton). 



