110 



MANUAL OF PHYSIOLOGY. 



fectly evenly and without any check or pause, the act of degluti- 

 tion is commonly divided into three so-called stages, between 

 which, however, it is by no means easy to draw a hard and fast 

 line. 



The first stage is simply the initiatory step of placing the morsel 

 of food or some liquid in such a position as to excite the second 



FIG. 53. 



Transverse section of CEsophagus (Horsley). a. Outer fibrous covc'riii.u;. 

 /. Hi indies of longitudinal muscle cut across, c. Transverse muscular coat 

 cut obliquely, d. Sub-mucous coat with glands in section, e. Musnilaris 

 inucosic. /. Mucous membrane with cut vessels, g. Stratified epithelium. 



or spasmodic act of deglutition. This first step is a voluntary 

 act, and it is the only part of the movements of swallowing over 

 which we have any voluntary control. The progress of the 

 morsel between the tongue and palate towards the fauces may be 

 as slow and gradual as we wish, but the moment a certain point 



