The Digestive System - 297 



SOFT PALATE 

 PHARYNX 



ESOPHAGUS 

 TRACHEA 



NASAL PASSAGES 



A, HARD PALATE 



NOSTRIL 



MOUTH 



JAW BONE 



TONGUE 



SALIVARY GLANDS 



LARYNX 



LEFT LUNG, SECTION 



ALVEOLI 

 A_ PLEURA 



STOMACH 



E in \ I SPLEEN 



iv^ \*A V / PANCREAS 



SMALL INTESTINE 

 ]Q DESCENDING COLON 



APPENDIX 



RECTUM t 



Fig. 16-11. Internal organs of man, with emphasis on the digestive and respira- 

 tory systems (semidiagrammatic). 



are poured upon the food while it passes 

 through the very first part of the small intes- 

 tine, and the intestinal juice, from the nu- 

 merous microscopic intestinal glands in the 

 intestinal wall, is added further along in the 

 tract. When the food mixture reaches the 

 large intestine, digestion has been completed 

 and most of the end products of digestion 

 have been absorbed. But while the remnants 

 of the food pass through the large intestine 



to the rectum (Fig. 16-11), much of the resid- 

 ual water is absorbed. Accordingly, when the 

 mass is egested through the anus, it usually 

 displays a semisolid consistency. 



Microscopic Structure of the Digestive 

 Tract. Although the various parts of the di- 

 gestive tract are superficially quite different, 

 all parts display a similar histological struc- 

 ture. In fact the enteron wall is formed 

 throughout by four concentric layers, which 



