ii6 



BIOLOGY OF THE LABORATORY MOUSE 



the nucleus the cytoplasm contains chromophil substance, staining intensely 

 with basic stains and causing vertical striations. The nucleus is relatively 

 large and round or oval in shape. Above the nucleus coarse zymogen 

 granules are present and can be demonstrated by special technique. Basal 

 cells are present between the epithelial cells and the basement membrane 

 (Fig- 52). 



Rodded epithelium 



Alveolus 



Intralobular duct 



-Parotid gland. (X200.) 



Digestive Tube 



The wall of the digestive tube is composed of several layers. The inner- 

 most layer is the mucous membrane or tunica mucosa, which consists of a 

 surface layer of epithelium and the underlying connective tissue, the 

 lamina propria (also called stratum proprium or tunica propria). In some 

 parts of the tube a layer of smooth muscle fibers, the muscularis mucosae, 

 forms the limit of the mucous membrane and separates it from the sub- 

 niucosa, which is composed of loose connective tissue. Where the mus- 

 cularis mucosae is not present the lamina propria changes gradually into 

 the submucosa. The muscularis externa, also called tunica muscularis, 

 consists of layers of muscle fibers. In the stomach and intestines this layer 

 is surrounded by the serosa, composed of a thin connective tissue membrane 

 and covered by mesothelium. The esophagus and the rectum are attached 

 to the adjacent tissue by a layer of loose connective tissue, the tunica 

 adventitia. 



Esophagus. — The esophagus is a tube which connects the pharynx with 

 the stomach. The stratified squamous epithelium lining the lumen con- 

 sists of a thin stratum germinativum, a somewhat heavier stratum gran- 

 ulosum and a stratum corneum which forms about one half of the total 



