THE ALIMENTARY CANAL 



169 



into the stratified squamous epithelium restinji; upon it. In addition 

 to the deep mucous glands found in the suhmucosa there may also 

 be simi)Ie branched tubular glands lying in the tunica proi)ria and 

 resembling those to be found in the cardiac portion of the stomach. 

 When the esophagus is contracted, the mucosa is disposed in longi- 

 tudinal folds and the lumen is closed. 







AdventiHa 



Fig. 106. — Diagram of a cross-section of a mammalian esophagus. 



The Stomach. —Beginning with the stomach and extending 

 through the large intestine, the adventitia is covered by mesothe- 

 lium, and the coat thus formed is called a serous membrane or 

 serosa. 



The Fish Stomach. ^The submucosa has broad ruga-like expan- 

 sions extending toward the center of the lumen. The mucosa con- 

 sists of closely packed, slender, simple columnar epithelium lining 

 the lumen and tubular glands of variable depth. (Fig. 107.) The 

 peripheral submucosa is not so dense as that adjacent to the epithe- 

 lium. The muscularis coat consists of a thick circular muscle 

 sheath and a thin outer longitudinal coat. The ad^'entitia is very 

 thin. Evaginations occur in the posterior region of the stomach 



