THE CIRCULATION OP THE BLOOD. 



259 



their course in a general way, without special reference to the 

 variations for each animal group : 1. These nerves emerge from 

 the spinal eord (upper dorsal region), and proceed upward 



ff^ I Accelerator Center in Me- 



1 ^^„^^ 



Superior Cervical Ganglion. 



Spinal Cord. 



Middle Cervical Ganglion. 



Inferior Cervical Ganglion. 



Baaal Ganglion in Region 

 of FiTBt Kib. 



Accelerator Nerves. 



Heart. 



Fig. 217.— Biagram to illustrate tlie origin, course, etc., of accelerator impulses. It 

 will be undei-stood that this is intended to indicate the general plan, and not pre- 

 cisely what takes place in any one animal. Thus, while the accelerator nerves 

 may arise in this way, it is not meant to be implied that the heart is actually sup- 

 plied by three nerves of such origin in any case. The arrows, as before, indicate 

 the path of the impulses. 



before being distributed to the heart. 2. They may leave for 

 their cardiac destination either at (a) the first thoracic (or basal 

 cardiac ganglion, as it might be named in this case), (6) the in- 

 ferior cervical ganglion, (c) the annulus of Vieussens, or (d) the 

 middle cervical ganglion. 



It follows that the heart may be made to do increased work 

 in three ways : First, the relaxation of a normal inhibitory 



