THE HEART 65 



survive, both may pass away ; but that only further anatomical 

 and physiological research can show. 



F. THE MOVEMENTS OF THE HEART IN SITU 



By virtue of the properties enumerated above the heart co- 

 ordinates itself to meet the circulatory needs of the body. More 

 research is needed before one can speak with certainty upon the 

 exact movements made by the heart in the unopened thorax, 

 although a considerable amount of work has been done on the 

 subject (Ludwig, Haycraft, Keith). As emphasised by Keith, the 

 heart has certain fixed fulcra from which it executes its normal 

 movements, and the moment the thorax is opened these are taken 

 away, and the true movements made by the heart are in part 

 obscured. These fulcra are as follows : 



(1) The venous mesocardium, or the part of the pericardium 

 attached around the great veins (Fig. 4, over a, i, i, and 6). 



(2) The arterial mesocardium, or the part of the pericardium 

 attached around the great arteries (Fig. 4, over g and /). 



Except at these two points the heart lies absolutely free 

 within the pericardium. But these mesocardia are attached to 

 the surrounding structures, and it is by this means that steadiness 

 is obtained. For instance, the part attached to the venous end 

 is bound to three structures : 



(1) To the root of the lungs, and by the lungs to the wall of 

 the thorax. 



(2) To the diaphragm, especially to the crura. 



(3) To the structures in the root of the neck through the fibrous 

 tissue surrounding the superior vena cava. 



Now to this fulcrum the longitudinal muscle of the auricle is 

 attached, and it is obvious that when the thorax is opened the 

 auricle can no longer perform its normal movement. 



As we have seen, the heart's excitatory wave arises in the great 

 veins, especially in the neighbourhood of the sino-auricular groove 

 between the superior vena cava and auricle. Of this there is 

 physiological proof, since, as stated above, it is only in this region 

 that the rhythm of the heart can be modified. The wave passes 

 from here to all parts of the heart, and they respond to it in 

 orderly sequence. We should expect, perhaps, that since it arises 

 in closer proximity to the right auricle, this auricle would contract 



E 



