INTERNAL ORGANS. 13 



tongue into the pharynx, it cannot fall into 

 the windpipe, on account of its being covered 

 by the valve epiglottis^ which is forced 

 down upon the windpipe by the food, as it 

 passes into the pharynx, so as to shut it com- 

 pletely. If at this instant the animal happen 

 to cough, that is, throw out air with conside- 

 rable force from the lungs, the valve is for a 

 moment opened by it, and a little of the food 

 or water is liable to get into the windpipe, 

 whence it is soon expelled by violent coughing. 



The oesophagus, having passed along the 

 throat and back part of the chest, penetrates 

 through the dit.^^ lii'agm, and terminates in the 

 stomach. 



The oesophagus of a horse has on its internal 

 surface an insensible membrane, which 

 stretches into the stomach, and lines nearly 

 one half of its surface : this peculiarity enables 

 us to account in some measure for the inac- 

 tivity of many violent poisons when given to 

 the horse. In the human oes^ophagus, this 

 membrane does not exist, the whole of its in- 

 ternal surface, as well as that of the stomach, 

 being exquisitely sensible. 



If two grains of emetic tartar be swallowed 

 by a man, they soon occasion violent vomiting j 



