54 VETERINARY STUDIES 



cular. It connects by openings with the nasal chambers above, 

 with the mouth in front, and with the esophagus behind, with 

 the lungs below, and on each side with the Eustachian tube to 

 the middle ear. 



Larynx. — A cartilaginous box located at the upper end of the 

 trachea and composed of five pieces — one epiglottis, one thyroid, 

 two arytenoids, one cricoid. Twelve muscles attach to these 

 cartilages for the purpose of controlling them. 



The epiglottis is a tongue-shaped piece of flexible cartilage 

 which aids in preventing food from entering the larynx during 

 the act of swallowing and then opens during respiration. 



The thyroid cartilage (shield-like) is located at the upper and 

 front portion of the larynx, extending well around on the sides. 



The arytenoids are two in number, one on each side. The two 

 taken together are shaped somewhat like the front part of a 

 pitcher, situated at the sides of the upper part of the larynx, 

 coming together at the median line. These cartilages give attach- 

 ments to the vocal cords. One of these cartilages, usually the 

 left, is paralyzed in the disease of horses which is known as 

 roaring. 



The cricoid is shaped like a ring with a process on the upper 

 and front part which causes this cartilage to resemble a seal 

 ring. It is located at the lower portion of the larynx and con- 

 nected with the trachea. 



The vocal cords are a pair of narrow fibrous bands so situated 

 as to include a narrow triangular space between them. They 

 are attached in front to the thyroid and behind to the aryte- 

 noids. 



Trachea, or windpipe. — This is located beneath and in front 

 of the esophagus. It is a long tube composed of about 50 car- 

 tilage rings and lined with mucous membranes. It begins at 

 the cricoid cartilage above and terminates in the bronchi below. 

 It therefore connects the larynx and bronchi. It is lined by a 

 mucous membrane which is covered by ciliated cells. 



Bronchi. — The bronchi are two in number, are branches of the 

 trachea, and very similar to it in structure and function. One 

 bronchus attaches to the root of each lung. 



Each bronchus divides into smaller and smaller' branches like 

 the branches of a tree. At the end of each terminal branchiole 

 there is a minute cavity, the air sac or alveolus, and making up 

 the wall of this alveolus are a large number of microscopic air 



