2Q8 



DIGESTION. 



disposed longitudinally ; those of the inner layer trans- 

 versely, or in portions of circles encompassing the canal. 

 They are composed of the unstriped kind of muscular fibre. 

 Between the mucous and muscular coats, there is a layer 

 of submucous tissue, in which numerous blood-vessels and a 

 rich plexus of nerves and ganglia are imbedded (Meissner) . 

 The mucous membrane is the most important coat in 



relation to the function of 

 digestion. The following 

 structures which enter into 

 the composition may be 

 now successively described; 

 the valvulat conniventes ; 

 the villi ; and the glands. 

 The general structure of the 

 mucous membrane of the 

 intestines resembles that 

 of the stomach (p. 266), 

 and, like it, is lined on its 

 inner surface by columnar 

 or Eetiform tissue [(fig. 72) enters 



7P.M& 



epithelium. 



largely into its construction ; and on its deep surface is a 



layer of the muscularis mucosa (p. a^6)."* 2*b7 ( 



ValvulcB Conniventes. 



The valvulrc conniventes commence in the duodenum, 

 about one or two inches beyond the pylorus, and becoming 

 larger and more numerous immediately beyond the en- 

 trance of the bile-duct, continue thickly arranged and well 

 developed throughout the jejunum ; then, gradually 

 diminishing in size and number, they cease near the 



* Fig. 72. The figure represents a cross section of a small fragment of 

 the mucous membrane, including one entire crypt of Lieberkuhn and 

 parts of several others : a, cavity of the tubular glands or crypts ; 5, one 

 of the lining epithelial cells ; c, the lymphoid or retiform spaces, of 

 which some are empty, and others occupied by lymph cells, as at d. 



