468 



APPLIED BIOLOGY 



I x 



the mouth-cavity beneath the tip of the tongue. The se- 

 cretions of the salivary glands will be described later when 



we study their work in connec- 

 tion with the digestion of foods. 

 389. The Pharynx or Throat- 

 cavity. Again using the hand- 

 mirror, notice that at the back 

 part of the mouth-cavity muscu- 

 lar folds extend downward from 

 the soft palate and bound later- 

 ally the passage from the mouth- 

 cavity to the throat-cavity. Be- 

 tween these folds on each side is 

 a round body, tonsil. These are 

 the organs which often become 

 enlarged during a " cold " in the 

 throat (tonsilitis) . They are not 

 known to have any essential 

 function, and surgeons frequently 

 remove them when they become 

 permanently enlarged. 



The pharynx opens above into 

 the post-nasal cavity behind the 

 FIG. 156. Diagrams showing so ^ palate; and below into the 



relations of respiratory and ali- eSOphagUS and the trachea or 

 mentary passages in a fish (7), i T f i i 



amphibian (//), reptile or bird windpipe. Refer back to your 

 (///), and man (IV). Arrow study of the throat of the frog. 



orZ T rra^ntro? A1S ' there P 6n int the P ha ^ X 



gans ; N, nostrils ; K, gill-slits ; the Eustachian tubes from the 



D, alimentary canal ; L lungs; earg> The pharynx is the Central 

 O, esophagus ; T, trachea ; V, . . 



backbone. (After Wiedersheim.) passage for communication be- 

 tween the nose-cavities and the 



trachea, and between the mouth-cavity and the esophagus, 

 thus providing for movement of air from the nose to the 

 lungs and of food from the mouth to the esophagus. 



