202 



THE VASCULAR MECHANISM. 



vagus proper and the other by the cervical sympathetic nerve, and these two 

 sets have opposite and antagonistic effects upon the heart. We find upon 

 examination that we can make the following statements concerning them : 



The one set, those belonging to the vagus proper, are inhibitory ; they 

 weaken the systole and prolong the diastole, the effect with a strong stimula- 



FIG. 74. 



IX 



s. v, a 



in 



Diagrammatic Representation of the Course of Cardiac Augmentor Fibres in the Frog: V.r., 

 roots of vagus (and ixth) nerve. G. V., ganglion of same. Cr., line of cranial wall. Vg.. vagus 

 trunk, ix., ninth, glosso-pharyngeal nerve. S. V. C., superior vena cava. Sy., sympathetic nerve 

 in neck. G. c., junction of sympathetic ganglion with vagus ganglion sending i. c. intra-cranial 

 fibres passing to Gasserian ganglion. The rest of the fibres pass along the vagus trunk. G 1 , 

 splanchnic ganglion connected with the first spinal nerve. (? n , splanchnic ganglion of the sec- 

 ond spinal nerve. An. V., annulus of Vieussens. A.sb., subclavian artery. G 111 , splanchnic gan- 

 glion of the third spinal nerve. ///., third spinal nerve, r.c., ramus communicans. 



The course of the augmentor fibres is shown by the thick black line. They may be traced from 

 the spinal cord by the anterior root of the third spinal nerve, through the ramus communicans 

 to the corresponding splanchnic ganglion G m and thence by the second ganglion G n the annulus 

 of Vieussens, and the first ganglion G 1 to the cervical sympathetic Sy. and so by the vagus trunk 

 to the superior vena cava 5. V. C. 



tion being complete, so that the heart is for a time brought to a standstill. 

 Sometimes the slowing, sometimes the weakening, is the more prominent. 

 When the nerve and the heart are in good condition it needs only a slight 

 stimulus, a weak current, to produce a marked effect ; and it may be men- 

 tioned that the more vigorous the heart, the more rapidly it is beating, the 

 easier it is to bring about inhibition. Although, as we have said, the effect 



