THE IXTESTIXAL CAXAL. 



1021 



The mucous membrane is thick, red, and highly vascular at the upper part 

 of the intestine, but paler and thinner below. Its inner surface is shaggy like 

 velvet ; this is due to the presence of minute processes called I'iUi. Next the 

 submucous coat is a layer of unstriped muscle fibres, the muscularis mucosce. 

 This thin layer from the sheep makes the " catgut " of commerce. Internal to 

 this is a quantity of retifonn tissue containing goblet-cells and migratory leuco- 

 cytes supporting tubular glands, blood-vessels, nerves, and lacteals. Most inter- 

 nally the uiucosa is covered by a single layer of columnar epithelial cells resting 

 upon a basement membrane. The prismatic cells contain granular protoplasm 

 and oval nuclei. The free ends of the cells are invested by a cuticular zone or 

 basilar border, a well-defined band exhibiting a fine vertical striation. Some 

 interpret these as parallel canals for absorption of chyle. 



The mucous membrane presents in its different parts the following structures : 



conniventes ; 



Villi; 



Intestinal true glands 



7 ^ 77 7 f Solitary glands ; 

 Intestinal lumph-folhcles | Agmil ^ ed glandS) w Peyer ^ patcne s. 



( Grlands of Lieberkilhn ; 

 \ Grlands of Brunner ; 



conniventes (valves of Kerkring, 1670), who gave the incorrect name, 

 conniventes (connivere, to close the eyelids) (Fig. 638) are permanent crescentic 

 folds of mucous membrane and submucosa ; 

 each contains two layers of mucous mem- 

 brane, placed back to back and separated 

 by the submucosa. They contain no part 

 of the muscular coats, and are not obliter- 

 ated by distention of the intestine. They 

 extend transversely across the axis of the 

 tube for about one-half or two-thirds of its 

 circumference. Some form complete circles 



i ,1 i -i FIG. 638. Diagram of valvulae conniventes. 



and others spirals; the spirals rarely may (Brinton.) 



Valvulae conniventes 



Vittiu 



Mucous membrane 



Sub-mucogai 



Circular muscular coat 



Longitudinal muscular coat 



FIG 639. Longitudinal section of human small intestine to show relations of villi, valvulae conniventes, 

 and muscular -coats. Schematic. (From Piersol.) 



extend two or three times around the internal circumference. This is of interest, 

 as a spiral valve is the characteristic of the intestine of certain fishes e. g. the 



