THE HEART 69 



aorta also, and it seems probable that in auricular systole the be- 

 ginning of the aorta swings back and to the right, while in systole 

 of the ventricle.s it moves forwards and to the left. Absolute 

 physiological evidence of this movement is wanting, but Keith 

 has pointed out : 



(1) That with the heart in situ, if the auricle be filled with 

 injection of wax, the aorta is pushed forwards and recedes when 

 it is emptied. 



(2) In mitral stenosis and cases where the left auricle is dilated 

 the aorta is pushed forward. 



(3) No other movements are available on anatomical con- 

 siderations. 



(4) There is a portion of the pericardium so arranged as to act 

 as a bursa for this movement. 



(5) The attachment of the musculature of the interauricular 

 septum is such that its only action can be to serve in this movement. 



Considering the musculature of the left auricle in more detail, 

 we find that, unlike the right auricle, there are no pectinate 

 muscles. This is due to its being developed as mentioned above, 

 mainly from the auricular canal. The place of the pectinate 

 musculature is taken by a series of muscular bands (Fig. 5) which 

 are inserted into the inferior vena cava, and through it into the 

 pericaridum and diaphragm. Chief of these bands is the left 

 tsenia terminalis (h, Fig. 5) which, arising in front at the superior 

 vena cava, sweeps round to the. left in the anterior wall of the 

 left auricle, and turns down between the auricular appendix and 

 left pulmonary veins, to end in the inferior vena cava. Above 

 and laterally the left auricle is attached to the roots of the lungs 

 by the pulmonary veins and the fibrous venous mesocardium 

 (xx, Fig. 5). The musculature of the left ventricle is essentially 

 the same as the right. The outer spiral fibres (Fig. 5) and the 

 inner longitudinal system again render the apex a fixed point. 

 The opponent to the auricular musculature is the longitudinal 

 system passing to the auricular part of the A-V groove. There is 

 therefore the same to-and-fro movement here the auricular mus- 

 culature in auricular systole draws the ventricle up (from A A' 

 Fig. 5), while by ventricular systole the A-V groove is drawn from 

 A' A, thereby expanding the left auricle and causing a negative 

 pressure. There should therefore be a rapid flow of blood from 

 the lungs to the left auricle during ventricular systole, but 



