COURSE OF THE INGESTA. 91 



that the two posterior pillars of the fauces * for a moment 

 approach the middle line, so as with the aid of the uvula to 

 shut off the nasal part of the pharynx from the lower por- 

 tion. By this means the food is thrown back into the lower 

 part of the pharynx, and thereupon, by the contraction of 

 the pharyngeal constrictors, it is propelled into the oesophagus, 

 and so into the stomach. At the same time that provision 

 is made to prevent the food passing up into the nose, the 

 windpipe is also effectually protected from the entrance of 

 the smallest particle. This is accomplished by the upward, 

 and forward movement of the hyoid bone, by which the 

 larynx is brought under cover of the root of the tongue, 

 and that part of the tongue, being also pulled backwards, 

 pushes with it the epiglottis, pressing it down over the 

 aperture of the air passage, while the contraction of a few 

 muscular fibres at the sides of that structure shut it down 

 completely like a lid. 



The propulsion of the food down the oesophagus is of the 

 same description as along the intestine. The oesophagus, as 

 has been mentioned, is surrounded with circular and longi- 

 tudinal fibres; the latter are outermost, as is the typical 

 intestinal arrangement; and in both intestine and oesophagus 

 what happens is this : the longitudinal fibres contract in 

 the part of the tube in which the food is, the circular fibres 

 contract immediately behind and over it, and thus the food 

 is forced on, and, as it travels, the wave of contraction travels 

 with it. In the intestine, this method of contraction is called 

 vermicular or peristaltic movement. 



60. The lower end of the oesophagus, a little to the left of 

 the middle line, pierces the diaphragm, as the arched muscular 

 partition is called which separates the thoracic from the ab- 

 dominal cavity, and it immediately terminates in the stomach. 



The Stomach is a large expansion of the alimentary tube, 

 which lies in great part under cover of the lower ribs of the 

 left side, but extends across the middle line. It is of curved 

 form, its upper surface being short and concave, its lower 

 long and convex. At its left end, called also the cardiac 

 extremity, it is expanded, and it gradually becomes narrower 



* They are tlie prominences corresponding to the edges of two 

 muscles, the palato-pharyngei. 



