310 THE NERVOUS REGULATION OF THE HEART 



system gives lodgment to a certain number of ganglion cells which 

 give origin to the efferent cardiac fibers and serve as the terminal 

 station for a number of afferent channels. It should also be mentioned 

 that this center, as mapped out at the present time, possesses solely an 

 inhibitor function. The co-existence in this region of an accelerator 

 zone has not been established as yet but may be surmised upon the 

 basis of indirect evidence. Since the nervous system is bilaterally 

 arranged, there are of course two centers and two sets of fibers, one on 

 each side of the median line of the body. 



The Efferent or Cardiomotor Fibers. These fibers are inhibitor 

 and accelerator in their function. The inhibitors reach the heart by 

 way of the vagus or pneumogastric system, and the latter by way of 

 the cervical spinal cord and the thoracic sympathetic ganglia. Both 

 actions, of course, are autonomic, i.e., they are not under the direct 

 control of the will. 



The inhibitor fibers were discovered in 1845 by E. H. and E. 

 Weber. 1 They are found in all vertebrates as well as in many in- 

 vertebrates. In man, their presence has been fully established by 

 Czermak, 2 Thanhoffer, 3 and others. They arise in the nucleus of the 

 vagus and follow the highway of this nerve to the heart. Moreover, 

 while they pursue a perfectly independent course in some animals, 

 such as the woodchuck (Simpson) , they are most frequently combined 

 with other fibers having an entirely different function. The cardiac 

 branches of the vagus are commonly designated as the superior and 

 inferior cardiac rami. The former arise from the cervical portion 

 of the vagus somewhere between the superior and inferior laryngeal 

 nerves, while the latter take their origin from the thoracic portion of 

 this nerve as well as from the nervus recurrens directly. Having 

 attained the region of the heart, they enter into relation with certain 

 fibers of the thoracic sympathetic system (nervus accelerans) to form 

 the plexus cardiacus which envelops the ascending portion and arch 

 of the aorta. From here they are distributed to the nerve centers 

 (Remak's) situated in the domain of the heart, as well as to the more 

 distant cardiac musculature. Those fibers which connect the nucleus 

 of the vagus with the intracardiac centers, constitute the preganglionic 

 path, and those which unite the intracardiac plexus with the muscle 

 substance, the postganglionic path. 



Division of the vagi nerves has been practised several times since the day of 

 Rufus of Epheus and Salenus. Willis and Lower observed toward the end of the 

 seventeenth century that this procedure leads to a more violent pulsation of the 

 heart, this result being attributed to a weakness of the heart. In 1838, Volk- 

 mann noted that an inhibitor effect upon the heart may be produced by stimula- 

 tion of the vagus nerve with a constant current. Budge employed an electro- 

 magnetic rotation apparatus with similar results, but failed to give an adequate 

 explanation of this phenomenon. 



1 Handb. der Physiol., iii, 1846. 



2 Prager Vierteljahrschr., 1868, 100. 



3 Centralbl. fiir die med. Wissensch., 1875. 



