MAMMALIA— PHYSIOLOGY 



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secretion that prevents the clotting of blood. In man, the watery- 

 secretion from the parotids contains the enzyme ptyalin^ while the 

 submaxillary and sublingual glands furnish the viscid mucin. 

 The salivary glands and the mucous glands lining the buccal cavity 

 furnish about three pints of saliva in twenty-four hours. 



Fig. 239. Section of a portion of a salivary gland, magnified 500 diameters. The 

 duct d divides into the two branches d' and d'\ one of which ends in the alveoli, a, a. 

 Neighboring alveoli, a', «', whose ducts are not in the plane of the section, are also 

 shown. (After Koelliker. From Hough and Sedgwick, Human Mechanism. Cour- 

 tesy of Ginn and Co.) 



Tongue. — The mammalian tongue is well supplied with tactile 

 and gustatory papillae. The human tongue has three kinds of 

 papillae. The filiform papillae are the smallest and are scattered 

 over the dorsal surface of the tongue except at its base. In the 

 Carnivora the conical tips of these papillae are heavily armed with 

 horny epithelium, so that it is possible by their use to scrape bones 

 clean of muscles and even tendons. There are about four hundred 

 fungi-form papillae found over the middle and front of the tongue. 

 They are bright red in color. The ariterior portion of the tongue 

 is sensitive to sweet substances., while the lateral portions are sensitive 

 to sour and salt. The circumvallate papillae, about twelve in num- 

 ber, lie near the base of the tongue in a v-shaped group. They are 

 richly supplied with nerve fibers and specialized sensory cells and 

 are especially sensitive to bitter substances. 



In the mouth the food is divided, moistened, formed into a ball 

 and prepared for swallowing. Some of the starch, acted upon by 

 ptyalin, the enzyme of saliva, is changed into maltose. 



