318 Canadian Record of Science. 



Beating in harmony with the sinus proper are the ter- 

 minations of the great veins leading into the sinus. It is 

 easy to see that their conjoined power, which, so to speak, is 

 the governing propelling force of the whole heart, is greater, 

 i.e., there is a larger wave of contraction, on the right side 

 than on the left. Now, it is to be observed, that in all those 

 cases in which the left vagus, under the influence of a weak 

 current, can arrest the left auricle and perhaps the left part 

 of the sinus and its associated veins, that inasmuch as the 

 right part of the sinus keeps pulsating, sooner or later the 

 left part is overcome; whereas, when the right part is 

 arrested, its wave is so large, its controlling force so great, 

 the left is of itself so weak, that its wave (also weakened) 

 may not be able to pass on to the sinus extension and auri- 

 cles ; moreover, this left part and its veins, as I have often 

 noticed when the heart is dying, ceases to pulsate before the 

 right part of the sinus and its veins. I would then explain the 

 greater effect of the right vagus as a rule by the character 

 of the contraction wave, associated with the right part of 

 the sinus and its associated veins, and by the fact that the 

 nervous supply to this seems to be chiefly from the right 

 vagus, rather than to any deficiency in the kind or number 

 of the inhibitory fibres in the left vagus ; both may supply 

 an equal number of such fibres, but if the supply be even 

 partially unilateral, then the results follow as I have 

 endeavoured to explain. 



Inasmush as the force of the auricles is very much 

 lessened by vagus stimulation, great weakening of the beat 

 of the sinus may suffice to arrest the auricles and ventricle 

 without complete arrest of the sinus ; in such cases, sinus 

 arrest is not the sole cause of the stop of auricles and ven- 

 tricle, nor absolutely essential to it. 



Intracranial Stimulation of the Vagus. —The peculiar inner 

 conformation of the skull of the sea-turtle, and its great 

 thickness and hardness, make examination of the roots of 

 nerves intracranially very difficult. One such examination 

 gave the following results : — 



Exp.— Rhythm 5-6. 



