EXAMINATION OF THE RESPIRATORY APPARATUS. 317 



approximately as far as the inferior line of insertion of the common 

 intercostal muscle, and extends from the summit of the scapula in front 

 to the hypochondrium behind. 



Auscultation of this region through the ileo- spinal and common 

 intercostal muscle will always reveal, except in very fat animals, the 

 vesicular murmur to a point as far Back as the eleventh intercostal 

 space. Nevertheless, this vesicular murmur is relatively feeble, and 

 becomes imperceptible beyond the eleventh rib. 



The middle zone comprises the most convex portion of the ribs, and 

 at this point the wall of the thorax is thinnest, while the lung below 

 is thickest. 



For these reasons the vesicular murmur is heard at its maximum 



Fig. 166.— The areas over which auscultation of the chest may be performed, 

 showing their extent, position and relations to the thoracic wall. 1, Upper 

 zone ; 2, middle zone ; 3, inferior zone ; 4, subscapular zone. 



intensity at this point. Towards the upper and lower limits of this zone 

 are found the great bronchial divisions, so that auscultation should 

 alwa3'S be practised with the greatest care at this point. The middle 

 zone occupies approximately one-third of the total depth of the thorax. 

 The vesicular murmur becomes weaker as one passes backwards, and 

 finally disappears at a considerable distance from the angle of the 

 hypochondrium, following a curved line the convexity of which is 

 directed • forwards, and which is continuous w^ith that limiting the 

 upper zone. 



These peculiarities are due to the anatomical arrangement and 

 mode of insertion of the diaphragm on the internal surface of the 

 hypochondrium. 



