36 THE VETERINARY SCIENCE. 



wards changes into the mucous membrane as it passes up into the 

 chambers of the head. 



Nasal Chambers or Chambers of the Head.— These give pas- 

 sage to the air from the nostril into the larynx or Adam's apple. 

 There are two of these chambers divided in the center by a thin 

 partition of cartilage called the septum nasi, these communicate 

 with the sinuses of the head. The horse cannot breathe through 

 the mouth on account of the formation of the throat, and this 

 compels him to always breathe through the nostrils. This is a 

 point which should be remembered. 



Larynx or Adam's Apple.— It is a box made of cartilage, 

 or gristle, gives passage to the air and is also the organ of 

 voice ; it is situated in the floor of the gullet. This box 

 has an opening on its upper side, which is guarded by a valve, 

 this valve is always open except when the animal is swallowing 

 food or water. When the food is being swallowed it passes over 

 the valve which closes the opening while the food passes over it. 

 This is important, for if the valve does not close properly and 

 either food or water drop into the windpipe it causes the animal 

 to have a fit of coughing, and is spoken of as the animal to have 

 the food going the wrong way. On the outside of this box of 

 cartilage is found several small muscles attached which help to 

 hold it in its place, it is lined inside by a continuation of the same 

 membrane, as in the chambers of the head. Along the inside of 

 this box is found what is called the vocal chords which come into 

 play when the animal is whinnying. These chords are not nearly 

 so well marked as in the human being, and if they or the 

 cartilage of the larynx become affected by disease it generally 

 gives rise to the disease called roaring. 



Trachea or Windpipe. — This is a tube which carries the air 

 down from the larynx to the bronchial tubes in the lungs. This tube 

 is made up of forty or fifty rings of cartilage which are united to 

 each other by strong elastic ligaments which gives the windpipe 

 its flexibilitv, that is, it can be bent in any direction almost like a 

 piece of elastic. In tracing the windpipe from Adam's apple it is 

 found to enter the chest where it terminates into two small tubes, 

 one going to the right lung and one to the left lung ; these are 

 called the bronchial tubes. 



Bronchial Tubes and Air Cells. — These are made up of the 

 same material as that of the windpipe, but are only about half the 



