MOVEMENTS OF THE HEAET. 41 



continues until the cavities of the auricles are completety filled, the blood coming in by 

 a steady current ; and, during the repose of the heart, the blood is also flowing through 

 the auriculo- ventricular orifices into the ventricles. When the auricles have become 

 fully distended, they contract quickly and with considerable power (the auricular sys- 

 tole), and force the blood into the ventricles, producing complete diastole of these cavi- 

 ties. During this contraction, the blood not only ceases to flow in from the veins, but 

 some of it is regurgitated, as the orifices by which the vessels open into the auricles are 

 not provided with valves. The size of the auriculo-ventricular orifices is one reason 

 why the greater portion of the blood is made to pass into the ventricles ; and, farther- 

 more, during the auricular systole, the muscular fibres which are arranged around the 

 orifices of the veins constrict them to a certain extent, which tends to diminish the reflux 

 of blood. There can be no doubt that some regurgitation takes place from the auricles 

 into the veins, but this prevents the possibility of over-distention of the ventricles. 



It has been shown by experiments that the systole of the auricles is not immediately 

 necessary to the performance of the circulation ; and the contractility of the auricles 

 may be temporarily exhausted by prolonged irritation, the ventricles continuing to act, 

 keeping up the circulation of blood. 



Action of the Ventricles. Immediately following the contraction of the auricles, by 

 which the ventricles are completely distended, we have contraction of the ventricles. 

 This is the chief active operation performed by the heart and is generally spoken of as 

 the systole. As we should expect from the great thickness of the muscular walls, the 

 contraction of the ventricles is very much more powerful than that of the auricles. By 

 their action, the blood is forced from the right side to the lungs by the pulmonary artery, 

 and from the left side to the system by the aorta. Eegurgitation into the auricles is pre- 

 vented 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 re- 

 pose 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, it raises itself up, the apex is sent for- 

 ward, 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 arrangement, the heart is moved upward and forward during its sys- 

 tole. The course of the fibres from the base to the apex is from right to left ; and, a 

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



The locomotion of the entire heart forward was observed by Harvey, in the case of 

 the son of the Viscount Montgomery. The young man, aged about nineteen years, suf- 

 fered a severe injury to the chest, resulting in an abscess, which on cicatrization left 

 an opening into which Harvey could introduce three fingers and the thumb. This 

 opening was directly over the apex of the heart. The action of the portion of the heart 

 thus exposed is described by Harvey in the following words : 



" We also particularly observed the movements of the heart, viz. : that in the dias- 

 tole it was retracted and withdrawn ; whilst in the systole it emerged and protruded ; 

 and the systole of the heart took place at the moment the diastole or pulse in the wrist 

 was perceived. To conclude, the heart struck the walls of the chest, and became promi- 

 nent at the time it bounded upward and underwent contraction on itself." 



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 eminently elastic, 

 and, as they receive the charge of blood from the ventricles, become enlarged in every 



