DISEASES OF THE RESPIRATORY ORGANS. 



By W. H. Harbaugh, V. S. 

 [Revised in 1903 by Leonard Pearson, B. S., V. M. D.] 



The organs pertaining to the respiratory function may be enu- 

 merated in natural order as follows : The nasal openings, or nostrils ; 

 the nasal chambers, through which the air passes in the head; the 

 sinuses in the head, communicating with the nasal chambers; the 

 pharynx, common to the functions of breathing and swallowing; 

 the larynx, at the top of the windpipe; the trachea, or windpipe; the 

 bronchi (into which the windpipe divides), two tubes leading from 

 the windpipe to the right and left lungs, respectively; the bronchial 

 tubes, which penetrate and convey air to all parts of the lungs; the 

 lungs. 



The pleura is a thin membrane that envelops the lung and lines the 

 walls of the thoracic cavity. The diaj^hragm is a muscular structure, 

 completely separating the contents of the thoracic cavity from those 

 of the abdominal cavity. It is essentially a muscle of inspiration, 

 and the principal one. Other muscles aid in the mechanism of 

 respiration, but the diseases or injuries of them have nothing to do 

 with the diseases under consideration. 



Just within the nasal openings the skin becomes gradually but per- 

 ceptibly finer, until it is succeeded by the mucous membrane. Xear 

 the junction of the skin and membrane is a small hole, presenting 

 the appearance of having been made with a punch; this is the 

 opening of the lachrymal duct, a canal that couA^eys the tears from 

 the eyes. Within and above the nasal openings are the cavities, or 

 fissures, called the false nostrils. The nasal chambers are completely 

 separated, the right from the left, by a cartilaginous partition, the 

 nasal septum. Each nasal chamber is divided into three continuous 

 compartments by two thin, scrolllike turbinated bones. 



The mucous membrane lining the nasal chambers, and in fact the 

 entire respiratory tract, is much more delicate and more frequently 

 diseased than the mucous membrane of any other part of the body. 

 The sinuses of the head are compartments which communicate with 

 the nasal chambers and are lined with a continuation of the same 

 membrane that lines the nasal chambers ; their presence increases the 

 volume and modifies the form of the head without increasing its 

 weight. 



The horse, in a normal condition, breathes exclusively through the 

 nostrils. The organs of respiration are more liable to disease than 

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