RESPIRATORY APPARATUS. 121 



Horse. The abdominal boundary is a line drawn from 

 the 16th intercostal space, crossing the middle of the thorax at 

 the 11th rib, to the olecranon. 



The vortex of the diaphragm lies slightly above the 

 of the thorax at the 8th intercostal space. 



Ox. In ruminants the field of percussion is small on ac- 

 count of the less number of ribs (13), which causes the dia- 

 phr3p--'i to lie farther forward. 



The abdominal boundary in this animal is a line drawn 

 from the 11th intercostal space, crossing the middle of the 

 thorax at the 9th rib, to the olecranon. 



Dog. In the dog the shoulder lies well forward, which 

 gives a larger field of percussion. The abdominal boundary of 

 the field extends to the 9th rib at the middle of the chest wall. 



Swine. In swine, percussion can rarely be employed, 

 as the thick layer of subcutaneous fat and the restlessness of 

 the animal greatly interfere. The abdominal boundary of the 

 field of percussion extends from the 11th rib to the olecranon. 



The normal pulmonary percussion sound is due to the 

 vibration of the thoracic w^all. the elastic pulmonary tissue and 

 to the air contained in the lungs. 



The intensity of the sound depends upon the 

 volume of the air-containing lung tissue which is set in vibra- 

 tion. It will vary with the force used in percussing, the 

 thickness of the chest wall and the volume of the part of the 

 lung vibrating. Accordingly, more force is employed in per- 

 cussing a thick-walled chest than a thin-walled one. 



As the normal percussion sound at the 

 boundaries of the field of percussion 

 merges gradually into a t >• m p a n i t i c or a dull 

 sound, the exact borders of the lungs can 

 not be definitely defined under the ham- 

 mer. 



