1909.] The Nerves of the Atrio-ventricular Bundle. 153 



belonged to independent systems, and were separated by a considerable 

 amount of connective tissue at the atrio-ventricular junction. In 1893, 

 ten years after Gaskell's work appeared, Stanley Kent (5) showed that 

 muscular connection did exist in the mammalian heart. He found in young 

 rats that there was at birth a well-defined continuity of atrial and ventricular 

 muscles. As age advanced there took place a considerable development of 

 connective tissue in the atrio-lventricular groove ; nevertheless, in adults 

 there still persisted well-marked bands of muscle tissue between the two 

 chambers over a considerable a/:ea of the atrio-ventricular groove, and in 

 particular at the junction of the atrio-ventricular septum. This muscular 

 connection varied in amount in different animals, yet could be demonstrated 

 in all ; but the exact location of these bands he did not definitely determine. 



In the same year there appeared the work of Wilhelm His, junior (6), 

 " Die Tatigkeit des embryonalen Herzens und deren Bedeutung fur die Lehre 

 von der Herzbewegung beim Erwachsenen." Here for the first time was 

 given the definite location of the atrio-ventricular bundle. His demonstrated 

 that in the earliest stages of development of the mammalian heart there 

 exists a continuous muscle union between the heart segments, and that the 

 primitive contraction goes on without the presence of ganglion cells. 

 Further, it was erroneous to suppose that this primitive continuity of 

 muscles was completely interrupted in the adult by connective tissue at the 

 atrio-ventricular groove ; that while a break did occur it was by no means 

 complete, for at a particular place in the atrio-ventricular septum muscular 

 union persists. This union is brought about by a strand of muscle fibres 

 which springs from the posterior wall of the right atrium, passes forward to 

 the atrio-ventricular groove lying in the upper part of the ventricular 

 septum, soon forking into right and left branches. The presence of this 

 bundle of His has been confirmed by many subsequent writers. 



The most important work on the atrio-ventricular bundle is that of 

 Tawara(l), " Das Reizleitungssystem des Saugetierherzens." This Japanese 

 investigator, working in Aschoffs laboratory in Marburg, published, in 1906, 

 a careful and exhaustive monograph on the macroscopic and microscopic 

 appearances of the bundle in a series of mammals. In it he demonstrated 

 the connections of the fibres of the bundle with the ordinary cardiac muscle 

 and the relation of the Purkinje fibres throughout the heart to the atrio- 

 ventricular fasciculus. His findings (7) may be summarised as follows : — 



(1) In man and all the animals examined, the Purkinje fibres or their 

 equivalents form the outspreading of a muscular system which unites the 

 atrial muscle to the ventricular muscle. This muscular system constitutes 

 the atrio-ventricular bundle. 



