112 BIOLOGY OF THE LABORATORY MOUSE 



the surface. The stratified squamous epithehum fining both waUs of the 

 circular groove lacks the superficial cornified cell layers and contains 

 numerous taste buds. These are barrel-shaped structures occupying the 

 thickness of the stratified epithelium. Two kinds of cells take part in their 

 formation : the tall peripheral supporting cells which have pale staining oval 

 nuclei, and the slender neuroepithelial cells which have dark staining, spindle- 

 shaped nuclei and end in hair-like processes. The former cells enclose a 

 small central opening, the taste pore, into which the hair-like processes of the 

 neuroepithelial cells project. The taste buds of the fungiform papiUae are 

 similar in structure, but dift'er in that they project below the epithelium into 

 the lamina propria (Fig. 49). 



Loose connective tissue forms the lamina propria, which is thin except 

 where it projects into and takes part in the formation of the fungiform and 

 vallate papillae. Below the propria is the musculature of the tongue. This 

 consists of vertical, longitudinal and transverse striated muscle bundles. 

 Blood vessels branch between the muscle layers, and in the lamina propria 

 capillaries are numerous. Only near the base of the tongue are glands pres- 

 ent, surrounded by and separating the muscle bundles. Those near the 

 vallate papilla are serous glands (the glands of Ebner) which have short ducts 

 opening at the base of the groove of the papilla. There are small lobules of 

 mucous glands farther laterally and also dorsally which open with short 

 ducts directly on the surface of the tongue. 



The pharynx. — The oral cavity opens caudally into the pharynx, which 

 connects it with the esophagus. The pharynx also serves as a connection 

 between the oral and nasal passages and the larynx. Except for a small 

 area, where the respiratory epithelium of the posterior nares persist, the 

 entire surface of the pharynx is lined by stratified squamous epithelium 

 with cornified superficial layers. The lamina propria is composed of dense 

 connective tissue and is directly continuous with the muscular wall, which 

 is composed of striated muscle fibers. Between the muscle fibers groups of 

 mucous glands are present which open to the surface through short ducts, 

 lined by stratified squamous epithelium. Lymphatic tissue is not 

 present (75). 



Submaxillary glands. — The submaxillary glands are two large lobes 

 which slightly overlap on the midventral line of the neck. They are com- 

 pound, branched tubulo-alveolar glands. Each lobe is divided into several 

 lobules which are surrounded by and separated from each other by con- 

 nective tissue membranes. The glands have an extensive duct system. 

 The main duct of each lobe opens on the floor of the mouth. At its orifice 



