THE CARDIAC NERVES. 



583 



course has been worked out physiologically in a number of 

 animals. Among the mammalia and, indeed, among different 

 animals of the same species there is some variation, but a general 

 conception of their origin and course may be obtained from 

 Figs. 243 and 244, which represent in a schematic way the 

 anatomical path taken by these fibers. They emerge from the 

 spinal cord in the anterior roots of the second, third, and fourth 

 thoracic spinal nerves. Accord- 

 ing to some authors they may 

 be found also in the fifth tho- 

 racic, the first thoracic, or even 

 the lower cervical spinal nerves. 

 They pass then by way of the 

 white rami to the stellate or 

 first thoracic ganglion (6), and 

 thence by way of the annulus 

 of Vieussens (ansa subclavia) (7) 

 to the inferior cervical ganglion. 

 A number of branches leave 

 the sympathetic S3^stem and the 

 vagus in this region to pass to 

 the cardiac plexus and thence 

 to the heart. The accelerator 

 fibers are found in some of these 

 branches, mixed in some cases 

 with inhibitory fibers from the 

 vagus. In the cat Boehm has 

 described a special branch (ner- 

 vus accelerans) which runs from 

 the stellate ganglion directly to 

 the cardiac plexus (Fig. 244). 



The preganglionic portion of some of the accelerator fibers ends 

 around the ganglion cells in the first thoracic ganglion, while 

 others apparently make their first termination in the inferior 

 cervical ganglion. The accelerator fibers may be stimulated in 

 the spinal roots in which they emerge (II, III, IV), in the annulus, 

 or in some of the branches that arise from the annulus or from 

 the inferior cervical ganglion (5, 3, 2). It will be borne in mind 

 that no accelerator fibers are found in the cervical sympathetic 

 above the inferior cervical ganglion. 



At various times investigators have asserted that accelerator fibers are 

 contained also in the vagus nerve. Tlius, it has been shown that, after the 

 paralysis of the inhibitory fibers in the heart by atropin, stimulation of the 

 vagus causes an acceleration of the heart. Little attention has been paid to 

 the physiology of these fibers, since it seems evident that the great outflow of 

 accelerators is made via the sympathetic system. 



Fig. 244. — Sketch to show the accel- 

 erator (and augmentor) branches from the 

 stellate gangUon (in the cat, left side): 1, 

 The ventral branch of the annulus (ansa 

 eubclavia); 2, small branch not constantly 

 present; 3, Boehm's accelerator uerve 

 (N. cardiacus e ganglio stellate). 



