CHAPTER VIII 

 DISEASES OF THE RESPIRATORY APPARATUS 



General Discussion. — The respiratory apparatus may be 

 divided into two groups of organs, anterior and posterior. The 

 anterior group, the nostrils^ nasal cavities, jAarynx, lanjnx and 

 trachea, is situated in the region of the head and neck. The 

 posterior group, the bronchial tubes and lungs, is situated in 

 the chest or thoracic cavity. 



The nostrils are the anterior openings of the air j)assages. 

 The nasal cavities are situated in the anterior region of the 

 head, and extend the entire length of the face. Each cavity 

 is divided into three long, narrow passages by the two pairs of 

 turbinated bones. The lining membrane is the nasal mucous 

 membrane, the lower two-thirds or respiratory portion differing 

 from the upper one-third, in that the latter j^ossesses the nerve 

 endings of the olfactory nerve and is the seat of smell. The 

 five pairs of head sinuses communicate with the nasal cavities. 

 Posteriorly and near the superior extremity of the nasal passages, 

 are two large openings, the guttural, that open into the pharyn- 

 geal cavity. 



The pharynx is a somewhat funnel-shaped cavity. The 

 walls are thin and formed by muscles and mucous membrane. 

 This is the cross-road between the digestive and respiratory 

 passages. In the posterior portion of the cavity there are two 

 openings. The inferior opening leads to the larynx and the 

 superior one to the oesophagus. All feed on its way to the 

 stomach must pass over the opening into the larynx. It is 

 impossible, however, for the feed to enter this opening, unless 

 accidentally when the animal coughs. The cartilage closing this 

 opening is pressed shut by the base of the tongue when the bolus 

 of feed is passed back and into the oesophageal opening. 



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