248 HISTOLOGY 



posed of four layers (i) tunica mucosa, (2) tela submucosa, (3) tunica 

 muscularis, and (4) tunica adventitia or tunica serosa. The parts which 

 are covered with peritoneum have a serous coat for their outer layer; the 

 parts imbedded in connective tissue have the adventitious coat instead. 



The tunica mucosa consists of epithelium, tunica propria, and the 

 lamina muscularis mucosa. The epithelium is the entodermal lining of 

 the tube, and is folded and inpocketed so as to form innumerable pits and 

 glands, varying in their nature in different parts of the tube. The tunica 

 propria consists of reticular tissue, which in places becomes characteristic 

 lymphoid tissue. It is set apart early in development as a layer with 

 abundant nuclei, thus differing from the underlying mesenchyma. At a 

 later stage the lamina muscularis mucosa, or muscle layer of the mucous 

 membrane, develops beneath it, separating it from the submucosa. The 

 muscularis mucosae is a thin layer of smooth muscle fibers. 



The tela submucosa (tela, tissue) is a connective tissue layer which 

 contains many blood and lymphatic vessels, and the ganglionated plexus 

 submucosus. 



The tunica muscularis usually consists of an inner circular and an outer 

 longitudinal layer of smooth muscle fibers, separated by a thin layer of 

 connective tissue which contains the ganglionated plexus myentericus. 



The tunica serosa is a connective tissue layer, covered by the peritoneal 

 epithelium. 



The layers enumerated are to be examined in the oesophagus, stomach 

 and intestine, which differ from one another histologically, since these 

 layers are variously modified. 



(ESOPHAGUS. 



The oesophagus is a tube about nine inches long, the several layers 

 of which are continuous anteriorly with those of the pharynx, and poste- 

 riorly with those of the stomach. The mucous membrane is thrown into 

 folds, except when the tube is distended by the passage of food; but the 

 muscularis merely thickens on contraction, so that it always forms a smooth 

 round layer (Fig. 242). 



The epithelium is thick and stratified like that of the pharynx. Its 

 outer cells are flattened in the adult, but in the embryo they include nu- 

 merous islands of tall ciliated cells, some of which are found at birth. The 

 basal surface of the epithelium rests upon connective tissue papillae or 

 ridges. 



The glands of the oesophagus are of two sorts, superficial and deep. 

 The deep glands (glandules msophagea produnda) develop as scattered 

 tubular downgrowths which pass through the tunica propria and muscu- 



