SECTIOlSr IV. 



DISEASES OF THE HEART AND LARGE BLOODVESSELS. 



GENERAL ANATOMICAL AND PHYSIOLOGICAL CON- 

 SIDERATIONS ON THE DISEASES OP THE HEART. 

 PHYSICAL DIAGNOSIS. 



The diagnosis of the diseases of the heart requires a perfect 

 knowledge of the anatomy of this organ and of its physiological 

 phenomena in the normal and in pathological conditions. In our 

 domestic animals there is much more difficulty than in man, because 

 the physical examination of the heart is hindered by many circum- 

 stances. In quadrupeds, in fact, the heart is more or less com- 

 pletely hidden by the upper attachments of the anterior members ; 

 its percussion can only be practised from the left side. In draught 

 horses possessing strong muscles, as well as in the fat pig, it is abso- 

 lutely impossible. In small animals, its volume varies- consider- 

 ably, according to the race and the individuals ; it is difficult to 

 establish its dimensions, even approximately; moreover the number 

 of pulsations do not permit us to define their characters. Before 

 studying the cardiac affections in particular, we shall explain the 

 principles upon which their diagnosis may be established. 



I. The relations of the heart vary according to their nature. In 

 the horse alone, the largest part of the left ventricle, that which 

 corresponds to the halfmoon-shaped depression of the lung, is in 

 direct relation with the costal wall — at the surface of the space 

 situated between the third and sixth ribs ; consequently, direct per- 

 cussion of the heart is possible. Cardiac dulness which is per- 

 ceptible above and behind the seventh rib (eight or nine centimetres 

 behind the posterior edge of the shoulder) is abnormal ; in medium- 

 sized animals its height is extended to about twelve centimetres 

 above the floor of the pectoral cavity ; but we must direct attention 

 to the fact that the cardiac dulness begins but three fingerbreadths 

 from the lower edge of the sternum (great pectoral). In the ox, 



(439) 



