182 



I'lIYSIOLOdV 



CHAP 



suffers a brief delay on reaching the auriculo-ventricular groove, 

 and is then propagated with extreme rapidity from base to apex 

 of the ventricles. 



II. The changes exhibited in the three principal diameters of 

 the ventricles, and the modifications of the internal conformation 

 of the heart during systole, can be estimated by direct observation 

 (Harvey), by approximate measurements (Ludwig),and by recording 

 apparatus (Boy and Adami). Not only the transverse diameter 

 which no one contests but the longitudinal diameter also, shorten 



during systole ; the sagit- 

 tal or antero - posterior 

 diameter seems on the 

 other hand to lengthen 

 a little although this 

 is contradicted by some 

 observers. It is certain 

 that during systole the 

 elliptical base of the 

 heart becomes almost 

 circular, and the apex, 

 which in rest is tilted to 

 the left, becomes perpen- 

 dicular to the centre of 

 the base, advancing to- 

 wards the thoracic wall. 

 The ventricles simul- 

 taneously undergo a 

 twist from left to right, 

 by which a portion of 

 the left ventricle wall 

 becomes visible, which 

 during rest is covered by 

 the wall of the left lung. 

 That these changes 

 of form in the ventricles 

 during systole depend 

 essentially, like those of 

 the auricles during presystole, upon the specific structure of the 

 myocardium, is shown by the fact that the same changes of form 

 and diameter can be observed in the mammalian heart, when 

 excised and placed upon a flat surface (Ludwig). 



The structure of the myocardium is so complicated that it 

 only lends itself to schematic representation, and not to exact 

 description. The more recent studies of Hesse and Krehl, follow- 

 ing on those of Ludwig and Henle, have, however, cleared up the 

 points of greatest physiological interest, which may now be briefly 

 summarised. 



Flu. ".I. Posterior view of same preparation as in preced- 

 ing tigure. (Allen Thomson.) u, Left ventricle ; l>, left 

 ventricle ; <, <', posterior interventricular groove ; <!, right 

 auricle ; c, left auricle ; /, superior vena cava ; g, g', 

 pulmonary veins cut short; It, sinus of great coronary 

 vein covered by muscular fibres ; It', middle cardiac 

 vein joining coronary sinus; /, inferior vena cava: f, 

 Eustachian valve. 



