406 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



change of form is thus produced ; the heart becomes a smaller and shorter, 

 but a more pointed, cone. The systolic narrowing from side to side is very 

 conspicuous. In a mammal lying on its back, this narrowing is accompanied 

 by some increase in the diameter of the heart from breast to back so that the 

 surface of the ventricles toward the observer becomes more convex. Thus the 

 base of the ventricles, which tended to be roughly elliptical during their 

 relaxation, tends to become circular during their contraction ; and the diameter 

 of the circle is greater than the shortest diameter of the ellipse, which latter 

 diameter extends from breast to back. At the same time, the area of the base 

 when circular and contracted is much less than when elliptical and relaxed. 1 

 Naturally, none of these comparisons io mathematical figures makes any pre- 

 tence to exactness. At the same time that the contracting heart undergoes 

 these changes, the direction of its long axis becomes altered. In animals in 

 which the heart is oblique within the chest, the line from the centre of the 

 base to the apex, that is, the long axis, while it points in general from head 

 to tail, points also toward the breast and to the left. In an animal lying on 

 its back, the ventricles when relaxed in diastole tend to form an oblique cone, 

 the apex having subsided obliquely to the left and toward the tail. As the 

 ventricles harden in their systole, they tend to change from an oblique cone to 

 a right cone ; the long axis tends to lie more nearly at right angles to the base ; 

 and consequently the apex, unfettered by pericardium or chest-wall, makes a 

 slight sweep obliquely toward the head and to the right, and thus rises up 

 bodily for a little way toward the observer. This movement was graphically 

 called by Harvey the erection of the heart. 2 It is accompanied by a slight 

 twisting of the ventricles about their long axis, in such fashion that the left 

 ventricle turns a little toward the breast, the right ventricle toward the back. 

 This twisting movement is probably due simply to the course of the cardiac 

 muscular fibres. 



Changes of Position in the Beating- Ventricles. The changes in form 

 imply changes in position. The oblique movement of the long axis implies 

 that in systole the mass of the ventricles sweeps over a little toward the 

 median line and also a little toward the head. The shortening of the long 

 axis implies that either the apex recedes from the breast, or the base of the 

 ventricles recedes from the back, or both. Of these last three possible cases, 

 the second is the one that occurs. The oblique movement of the apex is 

 accompanied by no recession of it; but the auriculo-ventricular furrow and 

 the roots of the aorta and pulmonary artery move away from the spinal 

 column as the injected arteries lengthen and expand, and, as the auricles swell, 

 during the contraction of the ventricles. During their diastole the ventricles 

 are soft ; they swell ; and changes of form and position occur which need not 

 be detailed now, as they are simply converse to those of the systole and have 

 been indicated already in dealing with the latter. 



1 C. Ludwig: "Ueber den Bau und die Bewegungen der Herzventrikel," Zeitschrift fur 

 rationelle Medizin, 1849, vii. p. 189. 



2 Op. tit., 1628, p. 22. Translation, 1889, p. 22. 



