DEGLUTITION. 191 



The second period of deglutition involves more complex 

 and important muscular action than the first. By a rapid 

 and almost convulsive series of movements, the food is made 

 to pass through the pharynx into the oesophagus. The 

 movements are now entirely beyond the control of the will, 

 and belong to the kind usually called reflex. After the ali- 

 mentary mass has passed beyond the isthmus of the fauces, 

 it is easy to observe a sudden and peculiar movement of 

 elevation of the larynx by the action of muscles which 

 usually depress the lower jaw, but which are now acting 

 from this bone as the fixed point. The muscles which produce 

 this movement act chiefly upon the hyoid bone. They are 

 the digastric (particularly the anterior belly), the mylo-hyoid, 

 the genio-hyoid, the stylo-hyoid, and some of the fibres of 

 the genio-glossus. It is probable, also, that the thyro-hyoid 

 acts at this time to draw the larynx toward the hyoid bone. 

 With this elevation of the larynx, there is necessarily an ele- 

 vation of the anterior and inferior portions of the pharynx, 

 which are, as it were, slipped under the alimentary bolus as 

 it is held by the constrictors of the isthmus of the fauces. 



Contraction of the constrictor muscles of the pharynx 

 takes place almost simultaneously with the movement of 

 elevation ; and the superior constrictor is so situated as to 

 grasp the morsel of food, and with it the soft palate. The 

 mechanism of this act was first fully described by Gerdy. 1 



According to this description, the pharynx closely and 

 suddenly embraces the velum with the base of the tongue, 

 entirely obliterates the lower part of its cavity, and forces the 

 alimentary bolus to pass out. It is easy to understand, 

 then, how readily the food, made into a yielding mass by 

 mastication and insalivation, and coated with slimy mucus, 

 can be made to pass through the isthmus of the fauces over 

 the membrane, which is covered also with a glairy secretion. 

 The middle and inferior constrictors the largest and most 



1 GERDY, Note sur les mouvements de la langue et quelques mouvements du Pha- 

 rynx. Bulletin des Sciences Medicales, Paris, 1830, tome xx., p. 33. 



