190 HANDBOOK OF PHYSIOLOGY. 



differing in this respect from the auricles, in which, even after their 

 complete contraction, a small quantity of blood remains. The shape of 

 both ventricles during systole undergoes an alteration when the chest is 

 opened, the diameter in the plane of the base being diminished, but the 

 length of the heart as a whole is not altered (Ludwig). Haycraft states 

 that the heart undergoes no change of shape in the unopened chest. 

 During the systole of the ventricles, too, the aorta and pulmonary 

 artery, being filled with blood by the force of the ventricular ac- 

 tion against considerable resistance, elongate as well as expand, and 

 the whole heart moves slightly toward the right and forward, twisting 

 on its long axis, and exposing more of the left ventricle anteriorly than 

 is usually in front. When the systole ends the heart resumes its former 

 position, rotating to the left again as the aorta and pulmonary artery 

 contract. After the whole of the blood has been expelled from the 

 ventricles, the walls are believed to remain contracted for a short period 

 before the rapid re-dilatation of the chambers begin. 



Action of the Valves. (1) The Auricula- Ventricular. The dis- 

 tention of the ventricles with blood continues throughout the whole 

 period of their diastole. The auriculo-ventricular valves are gradually 

 brought into place by some of the blood getting behind the cusps and 

 forcing them up; and by the time that the diastole is complete, the 

 valves are no doubt in apposition, the completion of this being brought 

 about by the reflux current caused by the systole of the auricles. This 

 elevation of the auriculo-ventricular valves is materially aided by the 

 action of the elastic tissue which has been shown to exist so largely in 

 their structure, especially on the ventricular surface. At any rate at 

 the commencement of the ventricular systole they are completely closed. 

 It should be recollected that the diminution in the breadth of the base 

 of the heart in its transverse diameters during ventricular systole is 

 especially marked in the neighborhood of the auriculo-ventricular rings, 

 and this aids in rendering the auriculo-ventricular valves competent to 

 close the openings, by greatly diminishing their diameter. The mar- 

 gins of the cusps of the valves are still more secured in apposition with 

 another, by the simultaneous contraction of the musculi papillares, 

 whose chordae tendinese have a special mode of attachment for this 

 object. The cusps of the auriculo-ventricular valves meet not by their 

 edges only, but by the opposed surfaces of their thin outer borders. 



The form and position of the fleshy columns on the internal walls oi 

 the ventricle no doubt help to produce the obliteration of the ventricu- 

 lar cavity during contraction; and the completeness of the closure ma} 

 often be observed on making a transverse section of a heart shortl} 

 after death, in any case in which rigor mortis is very marked (fig. 149) 

 In such a case only a central fissure may be discernible to the eye in th3 

 place of the cavity of each ventricle. 



