124 CLINICAL DIAGNOSTICS. 



In examining the trachea we should look out for scars 

 resulting from tracheotomy wounds. The 

 form of the trachea should also be noted. In chronic trachei- 

 tis of the ox the trachea may be shaped like a saber scabbard. 



Flattening of the trachea in horses is probably due to a 

 paralysis of the transverse muscle. 



On auscultation of the larynx or trachea, nor- 

 mally a stenotic sound is heard [like a German "ch"]. It is 

 due to a vibration of the vocal cords and laryngeal walls which 

 is produced by the air forced through the organ. It is heard 

 best at expiration. When the mucous membrane of the lar- 

 ynx is swollen and firm, this sound becomes very pronounced 

 and assumes a whistling or hissing character. If the swelling 

 of the laryngeal mucous membrane is loose, or deposits of exu- 

 date cover the membrane, the sound produced is rattling or 

 purring. 



IX. Percussion of the Thorax. 



To properly percuss the lungs a knowledge of their topo- 

 graphical position is essential. 



Anatomy. The lungs and heart do not occupy the whole of 

 the thoracic space. The abdominal viscera encroach upon a 

 greater part of it. The partition between the chest and abdominal 

 organs is the diaphragm. This organ is inserted, in the arc of a 

 circle, to the inner surface of the whole thorax, reaching in an 

 oblique direction from the sternum backwardly and upwardly to 

 the lumbar vertebrae. In the region of the sternum its points of 

 attachment are at the union of the ribs with cheir cartilages, far- 

 ther posteriorly, however, the diaphragm does not extend down as 

 far as the cartilages of the false ribs, but passes obliquely across 

 their inner surfaces until, finally, at the last rib, it finds attach- 

 ment at the superior end. The diaphragm arches forward from 

 its points of insertion, extending into the thoracic cavity in the 

 shape of a cone the apex of which reaches in the various ani- 

 mals, somewhat beyond the middle of the 7th or 8th rib. At 

 expiration the diaphragm lies with its muscular portion directly 

 against the lateral chest wall, the tendinous portion then forming 

 the partition. With the beginning contraction of the diaphragm 

 at inspiration the arch becomes flattened in that the organ is 

 drawn away from the inner wall of the chest. The space left 

 hy the receding diaphragm is immediately occupied by the sharp 



