en. \x. 



INHIBITION. 



251 



vagus trunk, it will be understood that the effect of the stimula- 

 tion of the vagus in the frog is not in all cases purely inhibitory, 

 but may be augmentor, according to the position where the 

 stimulus is applied, the intensity of the stimulus, and the con- 

 dition of the heart ; if it is beating strongly a slight vagus 

 stimulation will produce immediate inhibition. 



JugularGanjIion 



Ganglion 

 trunci 

 Vagi 



Vagus 



Roots of 



Spinal 



accessory 



^ Cervical 

 Sympathetic 



_hiferior Cervical 

 Ganglion 



Subctavian 

 Artery 



Annulus 

 Ganglion Stellatum 



A nt. root 

 id.Thoracic 

 Nerue 



Post, root 



Third 

 Thoracic 

 Ganglion 



Fig. 250. Heart nerves of mammal. (Diagrammatic.) 



In the dog, the augmentor fibres leave the cord by the second 

 and third dorsal nerves, and possibly by anterior roots of two 

 or more lower nerves ; they pass by the rami communicantes to 

 the ganglion stellatum, or first thoracic ganglion, and thence 

 by the annulus of Vieussens to the inferior cervical ganglion of 

 the sympathetic ; fibres from the annulus, or from the inferior 

 cervical ganglion, proceed to the heart (see fig. 250). 



