292 



AUGMENTATION OF THE BEAT. 



[BOOK 



may be at first diminished in force. And, occasionally, the beats 

 are increased both in force and in frequency: the result is augmen- 

 tation, not inhibition. But this is due to the fact that in the frog 

 the vagus along the greater part of its course is a mixed nerve 

 and contains fibres other than those of the vagus proper. 



158. If we examine the vagus nerve closely, tracing it up to- 



G 1 ?- 



FIG. 55. DIAGRAMMATIC EEPBESENTATION OF THE COURSE OF CARDIAC AUGMENTOK 

 FIBRES IN THE FROG. 



Vr. roots of vagus (and ixth) nerve. GV. 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.e. intracranial 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. G 11 splanchnic ganglion of the second spinal nerve. 

 An.V. annulus of Vieussens. A.sb. subclavian artery. G m splanchnic ganglion of 

 the third spinal nerve. III. third spinal nerve, r.c. ramus communicans. 



The course of the augmentor fibres is shewn by the thick black line. They may 

 be traced from the spinal cord by the anterior root of the 3rd 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 

 S.V.C. 



