MOVEMENTS OF THE ALIMENTARY CANAL 471 



deglutition, which is described as occurring in three stages. The 

 first stage includes the passage from the mouth into the pharynx. 

 The food being collected into a heap on the tongue, the tip of that 

 organ is placed against the front of the hard palate, and then the 

 rest of the tongue is raised from before back, so as to press the 

 food-mass between it and the palate, and drive it back through 

 the fauces. This portion of the act of swallowing is voluntary, or 

 at least is under the control of the will, although it commonly 

 takes place unconsciously. The second stage of deglutition is 

 that in which the food passes through the pharynx; it is the most 

 rapid part of its progress, since the pharynx has to be emptied 

 quickly so as to clear the opening of the air-passages for breathing 

 purposes. The food-mass, passing back over the root of the tongue, 

 pushes down the epiglottis; at the same time the larynx (or voice- 

 box at the top of the windpipe) is raised, so as to meet it, and thus 

 the passage to the lungs is closed; muscles around the aperture 

 probably also contract and narrow the opening. The raising of 

 the larynx can be readily felt by placing the finger on the large 

 cartilage forming " Adam's apple" in the neck, and then swallow- 

 ing something. The soft palate is at the same time raised and 

 stretched horizontally across the pharynx, thus cutting oft" com- 

 munication with its upper, or respiratory portion, leading to the 

 nostrils and Eustachian tubes. Finally, the isthmus of the fauces 

 is closed as soon as the food has passed through, by the contrac- 

 tion of the muscles on its sides and the elevation of the root of the 

 tongue. All passages out of the pharynx except the gullet are 

 thus blocked, and by a sharp contraction of the mylohyoid mus- 

 cles, in the floor of the mouth, such great pressure is put upon 

 the food-mass as to shoot it clear through the pharynx into the 

 opening of the esophagus. Liquids or very soft foods, under the 

 impetus given by the contraction of these muscles, are propelled 

 the whole length of the gullet to the sphincter which guards the 

 entrance to the stomach; more solid masses are thrown only into 

 the entrance of the gullet whence the third stage of swallowing 

 conveys them to the stomach. The muscular movements con- 

 cerned in this part of deglutition are all reflexly excited; food 

 coming in contact with the mucous membrane of the pharynx 

 stimulates afferent nerve-fibers in it; these excite efferent nerve- 

 fibers proceeding to the muscles concerned and cause them 



