THE EFFERENT CARDIAC NERVES 



191 



system are connected, whereas the fibers (postganglionic) arising from these 

 cells retain their excitability (cf. Chapter XXY). This method has been 

 employed also for the study of the ganglionic connections of the vagus fibers. 

 In a frog poisoned with nicotine, stimulation of the vagus trunk produces 

 no inhibition of the heart; but stimu- 

 lation of the nerves running in the 

 auricular septum under certain cir- 

 cumstances gives very marked weaken- 

 ing of the heart beat. The ganglion 

 cells of the venous sinus must there- 

 fore be regarded as a relay station for 

 the cardiac inhibitory fibers (F. B. 

 Hofmann). 



B. THE ACCELERATOR NERVES OF 

 THE HEART 



These arise from the sympathetic 

 (Fig. 67). They pass out of the spinal 

 cord in the upper four or five (most 

 of them in the second and third) thoracic 

 spinal roots, and run in the sympathetic 

 chain to the first thoracic ganglion (n). 

 The latter sends out two connecting 

 branches to the inferior cervical gan- 

 glion (I), or to the vagus (a), which 

 run on either side of the subclavian ar- 

 tery forming the annulus of Vieussens. 

 Either from the inferior cervical gan- 

 glion itself, or from the annulus, or 

 from the trunk of the vagus just below 

 the inferior cervical, the accelerator 

 nerves (#) are given off to join the car- 

 diac plexus. Besides, accelerator fibers 

 are found in the cervical portion of the 

 vagus, since with the inhibitory fibers 

 thrown out of function by atropine 

 poisoning vagus stimulation produces 

 an acceleration of the heart beat. The 

 accelerator fibers running in the sym- 

 pathetic are described by physiologists 

 as the accelerator nerves. 



Stimulation of the accelerator in- 

 creases the pulse frequency more or less 

 (v. Bezold, the brothers Cyon) accord- 

 ing as the frequency was previously 

 low or high. The absolute maximum 

 of frequency attainable by stimulation 

 of the accelerator mechanism is en- 

 tirely independent of the previous rate 



FIG. 67. The cardiac nerves of the dog, 

 after Ellenberger and Baum. a, united 

 vagus and sympathetic; b, vagus; c, con- 

 necting fibers between the vagus and the 

 inferior cervical ganglion of the sympa- 

 thetic; d, cardiac nerves springing from 

 the vagus; e, cardiac plexus; /, recurrent 

 laryngeal ; </, </', pulmonary plexus ; /, in- 

 ferior cervical ganglion; m, annulus of 

 Vieussens ; n, first thoracic ganglion (stel- 

 late ganglion); o, rami communicantes 

 from this ganglion to the lost cervical 

 nerves; p, rami communicantes to the 

 first and second thoracic nerves; g, car- 

 diac branch from the stellate ganglion; 

 r, trunk of the sympathetic in the thorax ; 

 s, rami communicantes to the spinal 

 nerves; s', intercostal nerves; v, phrenic 

 nerve; 16, heart; 17, innominate artery; 

 18, left subclavian vein; 19, aorta. 



