54 A Manual of Veterinary Physiology. 



assuming a concave surface towards the ventricle. This 

 appears to be only the case in the horse, and the informa- 

 tion is obtained by the researches of Chauveau and Colin. 

 The pulmonary valves, and probably the aortic, meet not 

 only at their free border but actually overlap. Chauveau 

 states that he has tried experimentally to hold back one 

 of the pulmonary valves, but the others have applied them- 

 selves so closely around the finger that it was impossible 

 to produce a patent opening. In the aorta it is probable 

 that overlapping does not occur to the same extent, and 

 here the the corpora Arantii are of value. When these 

 valves are not acting they lie towards the Avail of the 

 vessel, but do not in the aorta, as was at one time con- 

 sidered, cover the openings of the coronary arteries. 



The elastic recoil of the aorta does not exercise its entire 

 pressure upon the valves, for we observe that the diameter 

 of the aorta at its origin is greater than the aortic opening 

 from the ventricle, and so the muscular substance of the 

 heart bears largely the shock of recoil. 



The Cardiac Sounds are really four in number, but as they 

 are in pairs we recognise only two. The first sound is a 

 long one, due to the vibration of the auriculo-ventricular 

 valves and the muscle sound of the contracting ventricle. 

 The second sound is due to the closing of the semi-lunar 

 valves of the aorta and pulmonary artery; it is a short 

 sound. The two sounds are reproduced by the words ' lubb, 

 dn pp.' 



Various instruments have been designed for the purpose 

 of displaying in a graphic manner the movements of the 

 heart, both internal and external. The internal move- 

 ments are ascertained by means of an instrument termed 

 a cardiac sound, first used by Chauveau and Marty. It is 

 a tube containing two hollow balls : the air in these is com- 

 pressed when the cavities contract, and the compression 

 moves a lever placed in connection with the tube. The 

 instrument is passed into the right heart through the 

 jugular vein, and into the left ventricle through the caret id. 

 ljurdon Sanderson states that it causes no inconvenience to 



