DISEASES OF THE CIRCULATORY SYSTEM. 183 



and high-pitched, especially when associated with hyper- 

 trophy of the ventricles. It has been heard in mitral in- 

 sufficiency consequent upon dilatation of the left ventricle, 

 and also where the mitral valves are thickened or otherwise 

 changed, and where large collections of fibrinous clots have 

 been found among the cordse tendinea. In disease of the 

 tricuspid valve it has also been detected. 



Murmurs heard during the diastolic period, known as 

 i-entricular diastolic murmurs, are likewise due either to 

 disease of the auriculo- ventricular valves or of the arterial 

 orifices. 



When occurring at the auriculo-ventricular valves the 

 murmur is due to the passing of the blood from the 

 auricle into the ventricle through a constricted orifice, due 

 to disease of the tricuspid or mitral valves. It is a murmur 

 of constriction. 



When occurring at the arterial orifices it is due to regur- 

 gitation of the blood from the aorta or pulmonary artery 

 into the ventricles, owing to the insufficient closure of the 

 semilunar valves. 



Murmurs may be heard both during diastole and systole, 

 in which case they are said to be double. 



The usual pathological changes causing the double mur- 

 mur in the horse are aortic insufficiency and mitral con- 

 striction. 



(B.) Exocardial Murmurs. — The healthy pericardium is 

 smooth, and thus no sound is produced when the opposed 

 surfaces of the serous membrane come in contact. 



When, however, the pericardium is roughened, as it is 

 when inflamed, a sound is produced. This is pericardial 

 friction. 



It is rough, rubbing, or grating in character, and being 

 synchronous with the heart's action, is nearly always 

 double, though it may be heard during systole or diastole 



