318 RESPIRATORY APPARATUS. 



The inferior zone is very limited, and corresponds externally to the 

 inferior third of the thorax, and topographically to the cardiac lohe or 

 middle lohe of the lung and to the inferior portion of the posterior lobe. 



As these pulmonary lobes are of comparatively slight thickness, the 

 vesicular murmur is feeble. It can be heard over a trapezoidal space, 

 forming a jirolongation of the middle zone, but not below in the region 

 of the sternum or pectoral muscles. 



The fourth zone extends over the mass of the olecranian muscles. 

 It is of triangular form, in consequence of the inclination of the scapula 

 and humerus. Except in very fat animals the vesicular murmur is 

 readily audible through the muscular mass on the right side l)etter than 

 on the left, on account of the development of the right anterior pul- 

 monary lobe. 



On the left side the beating of the heart is heard al)ove the 

 pulmonary sounds. 



Clinically one may hear an exaggeration of the ordinary respiratory 

 murmur whenever the lung is actively exercised, as, e.t/., immediately 

 after trotting. This exaggeration, however, is often pathological. It is 

 known as " juvenile or supplementary respiration," when due to the 

 fact that some other portion of the lung is not acting. 



The respiratory murmur may be lessened in certain morbid con- 

 ditions, such as emphysema and congestion of the lung, and may com- 

 pletely disappear in pneumonia or broncho-pneumonia, a fact which 

 is even of greater significance. 



In various jDathological conditions the respiratory murmur may also 

 be modified. On the other hand, the movement of air in the bronchi 

 also produces various sounds of importance. 



A number of different bronchial sounds may be distinguished; these 

 include both inspiratory and expiratory sounds, for sometimes an ex- 

 piratory sound may become audible and clearly appreciable, or may 

 acquire characters of the greatest importance. 



The inspiratory sound may be strong, rough, rasping, painful, moist 

 or rattling. The pathological expiratory sounds may vary between 

 audible, strong, rough, prolonged, or rattling. The varieties of souffle, 

 or rattle, are the tubal souffle of inspiration or expiration (met with 

 in pneumonia or broncho-j)neumonia) ; the soft, deep-seated pleuritic 

 souffle (peripneumonia) ; the continuous cavernous souffle (met with in 

 tuberculosis) ; the broad amphoric souffle, in which the vibrations are 

 extensive and of metallic character (met with in pneumo-thorax). 



As to the varieties of rales which usually accomj^any these souffles, 

 they may all be met with in tuberculous animals, and comprise 

 crepitant and sub-crepitant, mucous, cavernous, snoring and sibilant 

 rales. 



