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HANDBOOK OF PHYSIOLOGY. 



lated nerve-fibres, Meissner^s plexus, with ganglion cells at its nodes, 

 occurs in the submucous tissue from the stomach to the anus. 



(4.) The mucous membrane is the most important coat in relation to 

 the function of digestion. The following structures, which enter into 

 its composition, may now be successively described : the valvultv conni- 

 ventes ; the villi ; and the glands. The general structure of the mucous 

 membrane of the intestines resembles that of the stomach (p. 347), and, 

 like it, is lined on its inner surface by columnar epithelium. Adenoid 

 tissue (fig. 255) enters largely into its construction; and on its deep 

 surface is the muscularis mucosce (mm, fig. 260), the fibres of which are 

 arranged in two layers: the outer longitudinal and the inner circular. 



Valvulce Conniventes. The valvulaa conniventes (fig. 256) commence 

 in the duodenum, about one or two inches beyond the pylorus, and 



Fig. 358. 



Fig. 257. Transverse section through four crypts of Lieberkiihn from the large intestine of the 

 pig. They are liued by columnar epithelial cells, the nuclei being placed in the outer part of the 

 cells. The divisions between the cells are seen as lines radiating from L, the lumen of the crypt; G, 

 epithelial cells, which have become transformed into goblet cells, x 350. (Klein and Noble Smith.) 



Fig. 268. A gland of Lieberkuhn in longitudinal section. (Brinton.) 



becoming larger and more numerous immediately beyond the entrance 

 of the bile duct, continue thickly arranged and well developed through- 

 out the jejunum; then, gradually diminishing in size and number, they 

 cease near the middle of the ileum. They are formed by a doubling 

 inward of the mucous membrane; the crescentic, nearly circular, folds 

 thus formed being arranged transversely to the axis of the intestine, and 

 each individual fold seldom extending around more than ^ or f of the 

 bowel's circumference. Unlike the rugae in the cesopnagus and stom- 

 ach, they do not disappear on distention of the canal. Only an imper- 

 fect notion of their natural position and function can be obtained by 

 looking at them after the intestine has been laid open in the usual 

 manner. To understand them aright, a piece of gut should be distended 

 either with air or alcohol, and not opened until the tissues have become 

 hardened. On then making a section it will be seen that, instead of 



