364 . THE HUMAN BODY. - 



' 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 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, 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 contraction of the mus- 

 cles 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 when the pharyngeal muscles contract the food 

 can be squeezed only into the oesophagus. The muscular 

 movements concerned in this part of deglutition are all re- 

 flexly excited; food coming in contact with the mucous mem- 

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

 jpse excite the centre of deglutition which is placed in the 

 dulla oblong ata, and from it efferent nerve-fibres proceed 

 , the muscles concerned and (under the co-ordinating influ- 

 ice of the centre) cause them to contract in proper sequence, 

 rhe pharyngeal muscles, although of the striped variety, are 

 but little under the control of the will; it is extremely diffi- 

 cult to go through the movements of swallowing without 

 something (if only a little saliva) to swallow and thus excise 

 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 re- 

 flex nature of the contractions of the pharynx, any food which 

 has once entered it must be swallowed: the isthmus of the 

 fauces is a sort of Rubicon; food that has passed it must 

 continue its course to the stomach, although the swallower 

 learnt immediately that he was taking poison. The third 

 stage of deglutition is that in which the food is passing along 

 the gullet, and is comparatively slow. Even liquid substances 



