On Muscular Motion and Animal Spirits 293 



begin in the septum and be gradually propagated in 

 the walls of the ventricles. No doubt, for first setting 

 the blood in motion there is need of a powerful con- 

 traction and jump of the whole heart ; while yet a 

 more gentle constriction of the ventricles may suffice 

 for keeping it going. 



For the further expulsion of the blood from the 

 heart, its septum and ventricles contract not only 

 as to their length but also as to their breadth ; for the 

 fissures or little excavations with which the cavities 

 of the heart are hollowed out, have a position which 

 suits the heart when constricted from all sides, as the 

 eminent Lower has noticed. And it tells in favour 

 of this that the fibres of the heart are attached all 

 round to the orifice of the great artery ; whence it 

 comes that in their contraction they pull the sides of 

 that orifice in all directions and open a wide door for 

 the blood bursting out. 



Nor should we omit to state that the long diameter 

 of the septum of the heart is not straight, but is 

 gibbous and convex on the right ; but in respect of 

 the left ventricle it is concave, or at least plane ; as 

 is shown in Plate III., Fig. 9. Now this form of the 

 septum conduces in no small degree to the propulsion 

 of the blood from the left ventricle to the remotest 

 parts of the body; for when the wall of the right 

 ventricle contracts, the blood thus compressed pushes 

 against the convex side of the septum, and the septum 

 meanwhile contracting by its own force, becomes 

 straighter, and still further narrows the space of the 

 left ventricle, as may be seen in Plate III., Fig. 9. 

 So that, in fact, the pressure of the contracting right 

 ventricle also contributes no little to the contrac- 

 tion of the left. 



It is further to be noted that as the contracted 



