THE RHYTHMIC AND PERISTALTIC MOVEMENTS 103 



a delay in the passage of each contraction over it might occur 

 just as ordinarily takes place at the auriculo-ventricular junction, 

 or every second contraction might pass, or every third, fourth, 

 etc., contractions. In alTcases the ventricle remained quiescent 

 until the auricular contraction reached it. These experiments 

 convinced me that the beat of the heart was due to a peristaltic 

 wave of contraction which started in the sinus and travelled over 

 the muscular tissue of the auricles to the ventricle and bulbus 

 arteriosus, the rate of travel being quicker in the bulged portion 

 of the auricles and in the ventricle than in the more unaltered 

 portions of the original muscular tube. Thus I came to the con- 

 clusion that the efficiency of the heart of the cold-blooded verte- 

 brate as a force pump could be explained by the nature of the 

 alteration of its muscular tissue in the course of development. 



I pointed out at the same time that between the sinus and 

 the ventricle on the dorsal side of the heart a flattened band of 

 tissue existed from which on each side the reticulated structure 

 of each auricle arose. This flattened band, which I called the 

 junction wall between the auricles, and McWilliam called the 

 sinus extension, has its muscles much more circularly arranged 

 than in the bulged portion of the auricles. In this band the 

 coronary vessels and large nerve trunks pass from ventricle to 

 sinus ; very frequently one of the coronary vessels passes free 

 from the rest and with it runs one of the nerves passing along 

 from sinus to ventricle. This nerve I called the coronary nerve, 

 it is only one among many others which are present in this band 

 of tissue. Experiment shows that its fibres belong to the right 

 rather than to the left vagus. 



With respect to the two parts of the auricles, namely this 

 flattened band and the bulged portion, I pointed out that if the 

 bulged part of the auricles was cut away, and this flattened band 

 alone left, no contraction passed into the ventricle from the 

 sinus, although all the nerves were in this band and the part in 

 the auriculo-ventricular junction where they entered was richest 

 in ganglion cells. On the other hand as long as the bulged por- 

 tion of the auricle was left even the very smallest piece the 

 contractions passed to the ventricle which responded to each one. 

 I also examined the atrio-ventricular junction itself, and found 

 that the ventral side close against the aorta was mainly respons- 

 ible for the sequence of the contraction wave to the ventricle, 



