STRUCTURE OF THE HORSE. ' 121 



the lid; the appearance of gi'ay hairs over the eyes and on the 

 forehead; pendulous lips, with a wrinkled appearance; the with- 

 ers become high and sharp; the chin, or lower jaw, begins to be 

 I^ointed; the animal becomes more or less sway-backed; the space 

 between the thighs increases, and there is a general appearance 

 of feebleness and decay. 



OESOPHAGUS. 



The oesophagns, or gnllet, is a mnsciilo-membranous tube, 

 lined with mucons membrane, the same in general character as 

 that which lines the different parts of the month. It extends 

 from the pharynx, which is simply a continuation of the ex- 

 treme back part of the month, to the stomach. Directly behind 

 the root of the tongue is the opening of the pharynx, and behind 

 this the oesophagus. 



The oesophagus has no other use than for the conveyance of 

 aliment from the pharynx to the stomach. The process of deglu- 

 tition, or swallowing the food, is performed in the following 

 manner: The masticated food gathers as a bolus at the root of 

 the tongue, which, by retracting, forces the pellet through the 

 isthmus faucium into the pharynx; the soft palate recedes back- 

 wards and uj^wards; the food is forced down the epiglottis, clos- 

 ing the larynx; finally the pharynx grasps the bolus and passes 

 it downwards into the oesophagus. The food is propelled along 

 the oesophagus by the peristaltic action of its muscular walls. 

 The act of deglutition is involuntary in the oesoiihagus, the food 

 travelling by peristaltic motion, caused by the successive con- 

 traction of its muscular fibers. 



THE STOMACH. 



The stomach of the horse is small in proportion to the size of 

 the animal. Its average capacity is about three gallons, while 

 the stomach of man, whose weight is hardly one-eighth of that 

 of the horse, contains frequently three quarts. When distended 

 the stomach resembles a bent tube, with two lateral dilatations, 

 divided by a central constriction into a left, or cardiac, and a 



