THE FORM OF THE HEART. 3 



vessels. When the ventricles contract they do so with a twisting movement, 

 their walls become rigid and corrugated, their apex and base approximate, the 

 descent of the base being greater than the ascent of the apex, and the arteries 

 and veins on their surface become prominent and tortuous. The auricles 

 become swollen with blood, and seem to push before them the retreating 

 ventricles at the base. The great arteries are distended and lengthened, beins 

 apparently drawn downwards at their origin by the contracting ventricles. 

 When, however, the ventricles expand, the aspect of all the parts is reversed. 

 The ventricles enlarge in every direction, but especially towards the base. 

 Their walls are flaccid and smooth ; and the arteries and veins on their surface 

 become straight and small. The auricles shrink, becoming pale and wrinkled, 

 and are in great part replaced by the ventricles, into which they empty their 

 blood. The great arteries lessen in size, and shorten and ascend at their origin, 

 being apparently raised by the upward enlargement of the ventricles. 



" The chief movement observable in the auricles is the sudden retraction 

 of the appendices, which almost instantly become refilled with blood as the 

 ventricles contract. There is a slight twisting movement of the whole heart 

 during systole, both on its longitudinal and on its transverse axis. By its 

 rotation on its transverse axis the apex of the heart is tilted forwards ; by its 

 rotation on the long axis, the left ventricle, which, during the diastole, looks 

 backward, is turned forwards. The combination of the two movements gives 

 to the apex a twisting movement from left to right and forwards." 



Sibson measured the change of form of the heart by placing a 

 millimetre scale across the organ, and noting the systolic and diastolic 

 measurements of its parts. By Ludwig x the heart of the cat was like- 

 wise measured in situ. He observed that in systole the antero-posterior 

 diameter increased, the apex-base diameter shortened, the transverse 

 diameter diminished, while the circumference of the base changed from 

 an ellipse to a circle. 



The following measurements are a type of his observations : — 



Diastole. Systole. 



Transverse diameter ... 28 mm. 22*5 mm. 



Antero-posterior diameter . . 16 - 5 „ 20 - 6 „ 



These measurements were taken with the animal in the horizontal position, 

 lying on its back. Now the position of the heart and the pressure of the 

 surrounding organs considerably affect the form of the heart. 



During the period of diastole the heart becomes a flaccid bag, and thus 

 passes entirely under the influence of gravity. When an excised frog heart is 

 so placed on a glass plate that the base rests on the plate, the organ is seen to 

 become smaller in systole while the apex rises forward. If the heart be placed 

 with its posterior surface on the plate, the base becomes rounded in systole, and 

 the apex lifts itself up from the plate. Lastly, if the heart be suspended with 

 the apex hanging vertically downwards, then, while the base becomes round, 

 the apex moves nearer to the base during systole. 



Since the pressure of the surrounding organs, and especially of the 

 lungs, influences the form of the heart, it is impossible to arrive at any 

 accurate knowledge of the normal variations, so long as the experimental 

 observations are conducted in abnormal conditions with the thorax 

 opened. To obviate this difficulty, Briicke z implanted needles into the 



1 Ztschr. f. rat. Med., 1849, Bd. vii. S. 20".. 



2 Sitzuwjsb. d. k. Akad. d. Wissensch., Wien, 1855, Bd. xiv. S. 348 ; " Vorlesungen, 

 1874, S. 172. 



