542 



CIRCULATION OF BLOOD AND LYMPH. 



completed by the Cyon brothers M. and E. Cyon * 1866. These 

 fibers when stimulated cause an increased rate of beat and are there- 

 fore designated as the accelerator nerve of the heart. Their 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. 223 and 224, 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. According to some authors, they 



may be found also in the fifth 

 thoracic and 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 (7) to the inferior cer- 

 vical ganglion. A number of 

 branches leave the sympathetic 

 system 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 (nervus accelerans) which 

 runs from the stellate ganglion 

 directly to the cardiac plexus 

 (Fig. 224). 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 accele- 

 rator 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. Thus, it has been shown that, after the 



* For the history and literature of the accelerator nerves see Cyon, article 

 "Cceur,"p. 103, in Richet's " Dictionnaire de Physiologic, " 1900; or Tiger- 

 stedt, "Lehrbuch der Physiologic des Kreislaufes, " 260, 1893. 



Fig. 224. Sketch to show the accel- 

 erator (and augmentor) branches from the 

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

 The ventral branch of the annulus ; 2, 

 small branch not constantly present ; 3, 

 Boehm's accelerator nerve (N. cardiacus e 

 ganglio stella to). 



