vii THE DIGESTIVE SYSTEM AND ITS FUNCTIONS 149 



thicker layer of circular muscle fibers, and within this the 

 submucosa ; the latter is a connective tissue layer containing 

 numerous blood vessels. There is no sharp line of division 

 between the submucosa and the connective tissue portion 

 'of the mucosa ; the latter is more dense, and contains more 

 cellular elements ; between the mucosa and submucosa are 

 large, irregular lymph spaces which frequently extend into 

 the folds. The existence of a muscularis mucosae has been 

 affirmed by some investigators (Howes, Grimm, Langer, 

 Ecker), but others (Valatour, Heidenhain, Gaupp) were 

 unable to verify the observation. At most this layer can 

 consist of but a few scattered cells. In sections which I 

 have studied there are connective tissue fibers just below 

 the epithelium which give an appearance very much like 

 that of a thin muscle layer, but I have been unable to con- 

 vince myself of the existence of muscle cells in that region. 



The epithelium of the mucosa consists of a layer of 

 cylindrical cells among which two varieties may be distin- 

 guished, the goblet or beaker cells, and the ordinary type of 

 absorptive cells. The goblet cells may be distinguished by 

 the large, oval vacuole, the inner end of which is filled with 

 a transparent, more or less granular substance, which prob- 

 ably gives rise to mucus. The nucleus is situated near the 

 base of the cell, and the part between the nucleus and the 

 inner globule is constricted, and contains several small vacu- 

 oles (Bizzozero). The absorbing cells are narrow, with an 

 oval nucleus near the base ; the outer free border is thick- 

 ened, and shows a cross striation due to minute rods. Ac- 

 cording to Bizzozero the mucous cells do not arise from the 

 transformation of cells of the ordinary type, as Paneth main- 

 tains, but are a distinct kind of cell. The young stages of 

 the goblet cells may be seen wedged in between the bases 

 of the other cells, and all intermediate stages between these 

 and the mature type may be traced. 



