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A MANUAL OF VETERINARY PHYSIOLOGY 



spleen. The diaphragmatic curve of the colon is also carried 

 back to a limited extent. But the chief result arising from the 

 backward movement of the diaphragm is that connected with the 

 circulatory system. Blood-pressure in the posterior vena cava 

 is increased, the phrenic veins are emptied, and the portal vein 

 is filled. The to-and-f ro action of this muscle is a most important 

 aid to the circulation. The limitation in movement of the 

 central portion of the diaphragm suggests that no flattening of 



Fig. 44. — Diagram of the Extent of the Chest in the Horse and Position 

 of the Diaphragm. 



The area B, C, D, E, is under the scapula and its muscles, and practically not 

 available for auscultation ; the surface A, B, E, F, is the available area of 

 the chest wall. The lung reaches to within a hand's breadth of the false 

 ribs. A, F represents the last rib ; B, E runs parallel to the posterior edge 

 of the triceps ; C, D corresponds to the position of the first rib. 



The diaphragm bulges into the chest centrally, thus separating the two 

 lungs. The curved dotted line falling from A to E represents the central 

 line of the diaphragm, and shows the extent to which it encroaches on the 

 chest. 



it occurs during inspiration, and this is supported by X-ray 

 inspection in smaller animals. The viscera behind the diaphragm 

 are affected by each of its backward and forward movements 

 (see Fig. 43). The abdominal contents bulge forward, as it 

 were, into the chest, and so behave, as has been described, like a 

 piston being driven to and fro (see Fig. 45) . 



The lungs contain more air during a deep than during ordinary 

 respiration, so that the chest cavity is automatically reduced in 

 size during an ordinary inspiratory effort in order to meet the 



