INNERVATION OF THE HEART. 279 



Such collections of nerve elements are called automatic centres, 

 and are made up, like all other origins of nerve force, of gangli- 

 onic cells. 



FIG. 122. 



Diagrammatic Plan of the Cardiac Nerve Mechanism. The direction of the impulses 

 is indicated by the arrows. Both right and left sides of the cut are used to show one 

 complete lateral half of the fibres. 



The heart of mammalian animals so soon ceases to beat, that 

 it forms an unsatisfactory subject for experimental inquiry. The 

 heart's innervation which will be seen to be a complicated pro- 



