SWALLOWING. 337 



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 pur- 

 poses. The food mass, passing back over the root of the 

 tongue, pushes down the epiglottis; at ths same time the 

 larynx (or voice-box at the top of the windpipe) is raised, so 

 as to meet this 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 its large cartilage form- 

 ing " Adam's apple" in the neck, and then swallowing 

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

 stretched horizontally across the pharynx, thus cutting off 

 communication with its upper, or respiratory portion, lead- 

 ing to the nostrils and Eustachian tubes. Finally, the 

 isthmus of the fauces is closed as soon as the food has 

 passed through, by the contraction of the muscles on its 

 sides and the elevation of the root of the tongue. All pas- 

 sages out of the pharynx except the gullet are thus blocked, 

 and when the pharyngeal muscles contract the food can 

 only be squeezed into the oesophagus. The muscular move- 

 ments concerned in this part of deglutition are all reflexly 

 xcited; food coming in contact with the mucous mem- 

 brane of the pharynx stimulates afferent nerve-fibres in it; 

 these excite the centre of deglutition which is placed in the 

 medulla oblongata, and from it efferent nerve-fibres proceed 

 to the muscles concerned and (under the co-ordinating in- 

 fluence of the centre) cause them to contract in proper se- 

 quence. The pharyngeal muscles, although of the striped 

 variety, are but little under the control of the will; it is ex- 

 tremely difficult to go through the movements of swallow- 

 ing without something (if only a little saliva) to swallow 

 and excite the movements reflexly. Many persons after 

 having got the mouth completely empty cannot perform the 

 movements of the second stage of deglutition at all. On 

 account of the reflex nature of the contractions of the 



