Journal of Agriculture. 



[lo Sept., 1908. 



is also guarded on each side by a valve, but the arrangement of the flaps 

 is different frorrx that found in the mitral and tricuspid valves. Each 

 of these valves is formed by three pouches, the free edge of each pouch 

 pointing away from the ventricle. The shape of these pouches has given 

 the name semilunar to these valves. 



Fig. 50. The heart with the right auricle and right ventricle opened by dissection. 

 I, 2, venae cavae entering left auricle; 3, right auricle; 4I, muscular pillar attached to 

 chordae tendineae; 5, flaps of tricuspid valve; 4, semilunar valve guarding entrance 

 to; 6, the pulmonary artery; 8, aorta; 10, portion of left auricle. (After 

 Halliburton.) 



The heart, as every one knows, beats rhythmically, that is, there is 

 a period of muscular activity called systole followed by an interval of 

 rest called diastole. The movements that take place in systole in a 

 mammal are too quick for the eye to follow ; but mechanical records of 

 these changes, as well as comparison with, the slower beating hearts of 

 lower animals, allow us to give the following description: — Svstole 

 commences in the great veins, close to their junction with the auricle, 

 and takes the form of a wave of muscular contraction rather suggesting 

 a quick but imperfect peristalsis. When the wave reaches the auricle 

 the thin walls of this chamber contract in a short quick " snap." Then 

 the muscular wave passes through the connecting substance between auricle 

 and ventricle and reaches the ventricle, which at once goes into powerful 

 contraction. This sequence occurs on each side in the same manner and 

 at the very same time. When the contraction of the ventricle is over 

 the heart passes into diastole. 



