THE ANATOMY OF THE HORSE 65 



bers of the head. The vocal chords which come into play 

 when the animal is whinnying are found along the inside of 

 this box. These chords are not nearly so well marked as in 

 the human being, and if they or the cartilage of the larynx 

 become affected it generally gives rise to the disease called 

 roaring. 



4. Trachea or Windpipe. — This is a tube which carries 

 the air down from the larynx to the bronchial tubes in the 

 lungs. It is made up of forty or fifty rings of cartilage which 

 are united to each other by strong elastic ligaments. They 

 give to the windpipe its flexibility, that is, the power to bend 

 in any direction almost like a piece of elastic. From Adam's 

 apple the windpipe enters the chest where it terminates into 

 two small tubes, one going to the right lung and one to the 

 left. These are called the bronchial tubes. 



5. Bronchial Tubes and Air Cells. — These are made up 

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

 about half the size. After passing into the substance of the 

 lungs they break up into other small tubes which pass all 

 through the lungs and terminate into what is known as the 

 air cells. These small tubes and air cells are lined inside by 

 a very thin mucous membrane, a continuation of the mem- 

 brane lining the other organs already mentioned. Just inside 

 this thin mucous membrane is found the capillary network 

 of the lungs, and while the blood is slowly passing through 

 this network of vessels it gives off to the air in the air cells 

 carbonic acid gas and takes in the oxygen from the pure air 

 while it is in the lungs. 



6. The Lungs are the most important organs of respira- 

 tion or. breathing. They are spongy, yellowish organs, two 

 in number, one situated on the right side and the other on 

 the left. The right lung is the largest because of the left one 

 having a hollow in its side for the heart. The lungs are sep- 

 arated by a partition known as the mediastinum, by the heart 

 which is in the folds of this partition, and also by the large 

 blood vessels and oesophagus. They are made up of light 

 elastic tissue and are full of air cells and tubes. While the 

 animal is alive they are very large and fill up nearly the 

 whole chest cavity, but after death they collapse and are not 

 nearly so large. Between the lungs and the ribs is found a 

 serous membrane called the pleura or the lining membrane 



