THE STOMACH AND INTESTINE. 265 



are situated in the basal portions of the cells. The basal portion of 

 each cell consists of nonstriated protoplasm, ending in a longer or 

 shorter process which extends to the basement membrane, or possibly 

 even penetrates it. The epithelial cells have the power of produc- 

 ing mucus, a phenomenon which, in the normal condition, rarely 

 embraces whole areas of epithelium ; these cells (goblet cells) are 

 usually surrounded by others which are unchanged (for details about 

 goblet cells see General Histology, p. 87). Throughout the entire 

 intestinal tract the epithelium forms simple, branched, and compound 

 tubular and alveolar glands. These are depressions lying in the 

 mucosa, and only in the duodenum extend beyond it into the sub- 

 mucosa. 



The mucosa consists of adenoid tissue, consisting of reticular 

 fibers and a fine network of elastic fibers, containing relatively few 

 cells. It fills the interstices between the glands, and often forms a 

 thin but continuous layer (granular layer of F. P. Mall) below the 

 glands. It is therefore obvious that the development of the 

 mucosa is inversely proportionate to the number and the density of 

 arrangement of the glands ; when the latter are present in large 

 numbers, as, for instance, in the stomach, the mucosa is reduced to 

 a minimum. In the small intestine it forms not only the perma- 

 nent folds, but also certain leaf-like and finger-like elevations 

 known as villi, which are covered with epithelium and project into 

 the lumen of the intestine, thus increasing to a considerable extent 

 the surface area of the mucous membrane. In the mucosa are 

 found small nodules of adenoid tissue. These are spoken of as 

 lenticular glands when occurring in the stomach, as solitary glands 

 when found in the upper portion of the small intestine and in the 

 large intestine. In the lower portion of the small intestine they are 

 grouped to form the agminated glands, or Peyer's patches, which, 

 when large, extend into the submucosa. In the external portion 

 of the mucosa there is found a thin, somewhat denser layer, known 

 as the stratum fibrosum (F. P. Mall), consisting mainly of white 

 fibrous tissue (Spalteholz) ; and external to this is a layer consisting 

 of two or three strata of unstriped muscle-fibers, the muscularis 

 mncostz. As a rule, it is composed of an inner circular and an 

 outer longitudinal layer. This arrangement is interrupted only 

 where the larger glands and follicles penetrate into the submucosa. 

 The epithelium with the glands, the mucosa with its lymph-nodules, 

 and the muscularis mucosae form together the mucous membrane, 

 or tunica mucosa. 



Below the mucous membrane is the connective-tissue submucosa. 

 This is characterized by its loose structure, and consequently affords 

 considerable mobility to the mucous membrane. In the small intes- 

 tine it forms a large number of permanent transverse folds known 

 as valvnlce conniventcs (Kerkring). In the submucosa of the 

 duodenum occur the secreting portions of Brunner's glands (gland- 

 ular duodenales), and in the small intestine the larger lymph-nodes 

 and Peyer's patches. 



