PHYSIOLOGY OF ALIMENTATION. 



The act of swallowing is usually divided into three parts 

 corresponding to the anatomical regions through which the 

 food has to pass, namely, the mouth, the pharynx, and the 

 oesophagus. But this division, it will be seen, is a purely 

 arbitrary one and therefore had best not be made. In its 

 passage through the mouth and the upper portion of the 

 pharynx the food may be kept under the control of the will. 

 After the food has come into the grasp of the involuntary 

 muscle fibres of the oesophagus its movement can no longer 

 be controlled voluntarily. Under ordinary circumstances, 

 however, with the exception of the voluntary formation of 

 the bolus, the entire act is involuntary, and is essentially 

 reflex in character. 



The best experimental observations that we have on the act 

 of deglutition are those of KRONECKER and MELTZER, 1 and 

 those of CANNON and MosER. 2 Although the experimental 

 methods adopted by these investigators are radically different, 

 their results agree in the main very well. 



Preparatory to the act of deglutition the material to be 

 swallowed is collected into a bolus through the combined 

 movements of the cheeks, teeth, and tongue. The bolus 

 rests for a moment on the dorsum of the tongue. According 

 to KRONECKER and MELTZER the chief factor concerned in 

 forcing food through the pharynx and oesophagus is the quick 

 and powerful contraction of the mylo-hyoid muscles, aided 

 by the simultaneous contraction of the hyoglossi muscles. 

 The contraction of these sets of muscles puts the bolus of 

 food as it rests on the dorsum of the tongue under high 

 pressure and shoots it in the direction of the least resistance 

 through the pharynx and oesophagus. By the contraction 

 of these muscles the epiglottis is also closed over the tracheal 



1 KRONECKER and MELTZER: Archiv fur Physiologie, 1880, p. 446; 

 ibid., 1883, Suppl. Bd., p. 337, 351. MELTZER: Journal of Experi- 

 mental Medicine, 1897, II, p. 457. 



2 CANNON and MOSER: Amarican Journal of Physiology, 1898, I, p. 

 435. 



