108 THE STOCK owner's ADVISER. 



delicate, pale, rose-colored mucous memLrane, the Schneiderian 

 memhrane. The horse, not being able to breathe through the 

 month, takes in the air by the nasal chambers only. It then 

 passes into the larynx, which is situated immediately behind and 

 below the nasal chambers, and at the anterior extremity of the 

 windpipe. This not onh' gives passage to air, but is the organ 

 of voice. The cartilages which form the larynx are seven in 

 number — three single ones and two pairs. The former are the 

 cricoid, thyroid, epiglottis; the hitter the arytenoid and cunei- 

 form cartilages. We make special mention of the epiglottis, 

 since its office is so important. It is situated in front of the 

 opening of the larynx, which it completely closes during the 

 passage of food through the pharynx into the oesophagus. It is 

 soft and leaf-shaped, and is so attached that, when the animal 

 swallows, it shuts down and backwards, so as to entirely close 

 the opening of the larynx. Thus the food and water, in their 

 passage to the stomach, are prevented from entering the lungs, 

 but go onward into the oesophagus; after which the elastic 

 muscles of the epiglottis in an instant throw it back to its origi- 

 nal position, and the windpipe is open again. The larynx is suc- 

 ceeded ])}' the trachea; running down the neck, it enters the 

 thorax, and terminates at the base of the heart, where it divides 

 into the right and left bronchi. It consists of forty or fifty 

 rings, the ends of which overlap posteriorly, forming a perfect 

 expansile tube. The entire trachea is lined by mucous mem- 

 brane. 



The lungs operate on the same principle as a pair of bellows. 

 When ihe cavity of the thorax is enlarged by the contraction of 

 certain muscles, the lungs become distended by drawing in air. 

 When the muscles relax, the lungs tend to collapse, expelling 

 most of their contained air. The blood, through respiration, is 

 cooled and loses watery vapor. It gains oxygen and loses car- 

 bonic acid gas, which the venous circulation has brought back 

 from all parts of the system. 



