19I4-] 



MECHANISM OF THE HEART-BEAT. 



293 



to them by the act of filHng, while others held and some do still that 

 coordination between the two pairs rested on a carefully adjusted 

 mechanism involving the passage of impulses over nervous channels. 

 The need for theories of this sort lay in the fact that no muscular 

 connection between the auricles and ventricles was known to exist. 

 But in 1883, W. Gaskell convinced himself that the conduction of 

 impulses in the heart must pass over muscular pathways, and Wool- 

 dridge and Tigerstedt contributed experiments which pointed to the 



Aortic Valve. 



Mitral Valve. 



Jranch to Anterior 

 Papillary Muscle. 



Left Division o 

 A- ;' Bundle. 



Branch to Posterior 

 Papillary Muscle. 



Branch to Apex. 



Fig. 3. Ox-heart. Injection with dilute India ink of the bursa-like 

 spaces surrounding the left branch of the A-V bundle. 



probability of Gaskell's contention. Ten years later (1893) Stanley 

 Kent and His, Jr., actually saw and described a bundle of connecting 

 muscular fibers. Since then (1893-1908) the existence of this struc- 

 ture, best called the auriculo-ventricular bundle, has been sufficiently 

 confirmed. It passes from the lowest level of the auricles, divides 

 into two and supplies a branch to each ventricle (Fig. 3). It has a 

 peculiar muscular structure. In some species it contains large neural 

 elements, but in man and the higher mammals only fine nerve fibrillge 



