164 THE DIGESTIVE SYSTEM 



Hal cells derived from embryonic ectoderm. There are long spindle- 

 shaped cells, called supporting cells, and among these are long, 

 tapering, sensory cells with hair-like external tii)s that project into 

 the opening to the fossa. Each of the sensory cells is connected 

 basally with a fiber of the gustatory nerve. Substances entering 

 the mouth in solution come into contact with the hair-like tips of 

 the sensory cells, which when stimulated give the sense of taste. 



Many serous and mucous glands are present in the tongue. 

 Serous glands, known as von Ebener's glands, are numerous in the 

 neighborhood of the foliate papillae and among the muscle masses. 

 The ducts from these glands open to the exterior through the 

 bottom of the fossa between the adjacent papillae. (Fig. 101.) In 

 the region of the circumvallate papillae there are present in many 

 mammals mucous as well as serous glands. 



Salivary Glands.-^ In addition to the numerous small glands scat- 

 tered in the mucosa and underlying connective tissue of the oral 

 cavity, there are in mammals three pairs of salivary glands which 

 arise from the walls of the embryonic oral cavity as epithelial buds. 

 These three pairs of glands, the parotid, submaxillary, and sub- 

 lingual, display marked histological variation even in closely related 

 species. Their secretions are poured into the mouth as saliva in 

 response to various stimuli, and serve to keep the oral surface moist 

 and to lubricate the food. 



Parotic] Glands. — ^ear the base of each external ear is the largest 

 of the salivary glands, the parotid, whose main excretory duct opens 

 into the oral cavity. (Fig. 103.) The lobes and lobules into which 

 the gland is divided are supported by a relatively dense inter- 

 lobular fibroelastic connective tissue in which a branching system 

 of excretory ducts is located. The largest ducts are lined with a 

 stratified columnar epithelium, and their main branches haxe a 

 single layer of columnar cells. Adjoining the smallest excretory 

 ducts there are the so-called secretory ducts which occiu" within the 

 lobules. The secretory portions are composed of cohnnnar epithe- 

 lial cells with striated basal portions. The secretory ducts divide 

 into intercalated or intermediate ducts, which are very small and 

 formed of cuboidal cells. These terminate in the secreting end- 

 pieces where there are relatively large pyramidal cells of the serous 

 type with rounded nuclei more or less centrally located. The 

 lumens in these secreting end-pieces are ^'ery small. The whole 

 field presents a uniform appearance as regards the secreting cells, 

 a condition which is usually not a])]iar(Mit in (>itlicr of the other 

 salivary glands. 



