ZOOLOGY. 



the ears by a peculiar mechanism, and by their direction; 

 the opening leading to the larynx and air ]ia->age or trachea 

 is protected by a cartilage of a singularly wonderful mecha- 

 nism, closing the air tube hermetically whilst the food is 

 I'.i-sing over its upper surface; the gullet is then tin- only 

 aperture left by which the food can escape from the pharynx, 

 and this leads directly to the stomach. The movements and 

 contractions required to effect these actions are numerous, 

 complex, and quite involuntary; when disturbed, the food 

 may penetrate into the larynx and windpipe, causing for an 

 instant terrible distress, and certain death if not speedily 

 relieved. Finally, the gullet being in part muscular, by its 

 contractions the food is readily propelled into the stomach. 

 It is almost needless to say that the gullet is nearly straight, 

 and that the food does not descend into the stomach by its 

 own gravity. 



Stomachal Digestion or Chymificati'in. 



62, The food is changed in the stomach into the sub- 

 stance called Chyme. The stomach (Fig. 24) is a mem- 

 branous bag placed transversely in the upper part of the 

 abdominal cavity, and almost immediately below the dia- 

 phragm ; in man it has the shape of a bagpipe, and indeed it 

 is with the stomachs of animals having this shape that the 

 air reservoir of the bagpipe is made. It diminishes gradually 

 from left to right, and is curved on itself, so that its upper 

 edge is short and concave, its inferior, called the greater cur- 

 vature of the stomach, convex and long. By an opening 

 called cardiac (or, better, oesophageal), it communicates with 

 the gullet ; the opening leading into the small intestine is 

 called pyloric. The walls of the stomach are very dilat- 

 able; when empty, a number of folds may be seen internally, 

 which disappear when the stomach is full. Little follicles 

 or cavities maybe seen also. The term pylorus is derived 

 from the Greek word TruXovpos, a porter (71-^X77, a gate, and 

 ovpbs, guardian). During digestion, in the stomach the 

 pyloric orifice is closed, and afterwards opens to allow of tin- 

 passage of the chyme into the intestine ; over the interior of 

 the stomach are numerous small cavities called i/ttaf/'ic fol- 

 licles, which pour out upon the food the liquid they secrete. 



This liquid is the gastric juice, the most important of all 

 the agents of digestion, for by it the food is converted into 

 divine. So long as the stomach is empty, it is secreted 



