3o8 THE ANIMALS AND MAN 



has been added. Test a bit of soda cracker for its starch reaction 

 (see p. 297). Place the soda cracker (a little boiled starch will do 

 as well) in each of the three test tubes and leave over night in a warm 

 room. In the morning test the contents of each tube for starch and 

 for sugar. In which has digestion taken place? 



Deglutition. — Deglutition is the act of swallowing. Fig. 

 157 shows how it is begun. The tongue is raised to the 

 roof of the mouth, and the uvula automatically closes the 

 nasal passage. The food is pushed into the pharynx by 

 means of the muscles at the base of the tongue. 



The pharynx. — There are seven openings into the pharynx; 

 one each to the mouth, the windpipe or larynx, and the 

 oesophagus, a pair to the nasal passages, and a pair to the 

 Eustachian tubes leading to the middle ear. The opening 

 into the larynx (or glottis) is closed by the epiglottis during 

 deglutition. 



The pharyngeal cavity is lined with mucous membrane. 



The oesophagus, — The pharynx narrows into the elongated 

 oesophagus. This is also lined with mucous membrane and 

 has muscular walls which by peristaltic contraction pass the 

 food into the stomach. Peristaltic contraction is a contrac- 

 tion that starts at one end of a series of muscles and moves 

 along the muscles in a wave. It may be imitated by press- 

 ing the fingers on a rubber tube and drawing them the 

 length of the tube. 



The abdominal cavity. — This is the large cavity shown in 

 fig. 159 separated from the thorax or chest by the muscular 

 diaphragm (D). At the back are the spinal column and 

 lower ribs. Its base is formed by the large pelvic bones (P). 

 The sides and front are covered with muscles. The cavity 

 is lined with peritoneum, a membrane which is deflected 

 over the organs lying in this region, and which supports 

 them. This membrane secretes a fluid {serous fluid) which 

 keeps it moist. 



Form and structme of the stomach (figs. 156 and 159).— 



