MOVEMENTS OF THE HEART. 39 



tion into the auricles is prevented by the closure of the tricuspid and mitral 

 valves. This act accomplished, the heart has a period of repose, the blood 

 flowing into the auricles, and from them into the ventricles, until the auricles 

 are filled and another contraction takes place. 



Locomotion of the Heart. The position of the heart after death or during 

 the repose of the organ is with its base directed slightly to the right and its 

 apex to the left side of the body. With each ventricular systole, the apex 

 is sent forward and is moved slightly from left to right. The movement 

 from left to right is a necessary consequence of the course of the superficial 

 fibres. The fibres on the anterior surface of the organ are longer than those 

 on the posterior surface, and pass from the base, which is comparatively fixed, 

 to the apex, which is movable. As a consequence of this anatomical ar- 

 rangement, the heart is moved upward and forward during its systole. The 

 course of the fibres from the base to the apex is from right to left ; and as 

 they shorten, the apex is of necessity slightly moved from left to right. 



The locomotion of the heart takes place in the direction of its axis and is 

 due to the sudden distention of the great vessels at its base. These vessels 

 are elastic, and as they receive the charge of blood from the ventricles, they 

 become enlarged in every direction and consequently project the entire organ 

 against the walls of the chest. This movement is aided by the recoil of the 

 ventricles as they discharge their contents. 



Twisting of the Heart. The spiral course of the superficial fibres involves 

 another phenomenon accompanying its contraction ; namely, twisting. By 

 attentively watching the apex, especially when the action of the heart is 

 slow, there is observed a palpable twisting of the point upon itself from left 

 to right with the systole, and an untwisting with the diastole. 



Hardening of the Heart. If the heart of a living animal be grasped by 

 the hand, it will be observed that at each systole it becomes hardened. The 

 fact that it is composed almost exclusively of fibres resembling very closely 

 those of the voluntary muscles, explains this phenomonen. Like any other 

 muscle, it is sensibly hardened during contraction. 



Shortening of the Ventricles. The point of the heart is protruded during 

 the ventricular systole, but this protrusion is not due to elongation of the ven- 

 tricles. By suddenly cutting the heart out of a warm-blooded animal and 

 watching the phenomena which accompany the few regular movements which 

 follow, it is seen that the ventricles invariably shorten as they contract. This 

 can easily be appreciated by the eye, but more readily if the point of the or- 

 gan be brought just in contact with a plane surface at a right angle, when, at 

 each contraction, it is unmistakably observed to recede. During the inter- 

 vals of contraction, the great vessels, particularly the aorta and pulmonary ar- 

 tery, which attach the base of the heart to the posterior wall of the thorax, 

 are filled but not distended with blood ; at each systole, however, these ves- 

 sels are distended to their utmost capacity ; their elastic coats admit of con- 

 siderable enlargement, as can be seen in the living animal, and this enlarge- 

 ment, taking place in every direction, pushes the whole organ forward. It is 

 for this reason that, in observing the heart in situ, the ventricles seem to elon- 



