70 FEEDING ANIMALS. 



by which air can be introduced to the trachea, by reason of 

 the large development of the soft palate, which prevents 

 the entrance of air by the mouth. These orifices are, for 

 this reason, larger than in other domestic animals that 

 make use of the mouth as well as nostrils for the admis- 

 sion of air. 



The nasal cavities contain the olfactory membrane and 

 nerves, which give the sense of odors, besides other less im- 

 portant membranes, and conduct the air to the larynx, 

 which is a cartilaginous framework, forming a tube in- 

 tended for the passage of air during the act of respiration. 

 It has also the power of dilating and contracting to ac- 

 commodate the volume of air introduced into or expelled 

 from the lungs, and when partially paralyzed causes what is 

 called "roaring." But the most interesting office of the 

 larynx is as an air organ for the articulation of sounds. 



The trachea is a flexible and elastic tube, formed of a 

 series of cartilaginous rings, which connect with and con- 

 tinue the larynx and terminate above the base of the heart 

 in two divisions called the bronchi. 



Each of the two bronchi, or terminal branches of the 

 trachea, join to and imbed themselves in the substance 

 of the lungs. Their substance is cartilaginous like the 

 trachea. 



The thorax, or pectoral cavity, holds not only the lungs, 

 but the heart and the large vessels that spring from or 

 pass to the heart, with a part of the aesophagus. trachea and 

 nerves. The thorax rests upon and is surrounded by the 

 ribs, sternum and the dorsal vertebrae, and is above the dia- 

 phragm. It performs an important part in respiration. 

 It is dilated and contracted by the movements of the dia- 

 phragm and ribs. The lung is applied against the thor- 

 acic walls, and follows this cavity in its movements, dilat- 

 ing and contracting with inspiration or expiration. 



