190 



ACCELERATOR NERVES. 



[BOOK 



of the cervical spinal cord. The effects produced, however, are 

 very complex, and led, on their first being made known, to much 

 discussion, one outcome of which was the discovery of certain 

 nerves of a very peculiar character, which pass from the cervical 

 spinal cord, frequently along the nerve accompanying the vertebral 

 artery, and reach the heart through the last cervical and first 

 thoracic ganglia; these have been called the 'accelerator nerves.' 

 Their course is different in the rabbit and in the dog, see Figs. 41 

 and 42, and indeed varies even in the same kind of animal. 

 Stimulation of these nerves with the interrupted current causes a 

 quickening of the heart's beat, in which what is gained in rate is 

 lost in force, for the blood-pressure is not necessarily increased, but 

 may remain the same, or even be diminished ; apparently not only 



Trad, 



FIG. 41. THE LAST CERVICAL AND FIRST THORACIC GANGLIA IN THE BABBIT. (Left 

 side.) (Somewhat diagrammatic, many of the various branches being omitted.) 



Track. Trachea. Ca. carotid artery. s&. subclavian artery, n. Vag. the 

 vagus trunk, n. rec. the recurrent laryngeal. sym. the cervical sympathetic nerve 

 ending in the inferior cervical ganglion, gl. cerv. inf. Two roots of the ganglion 

 are shewn, rad., the lower of the two accompanying the vertebral artery, A. vert., 

 being the one generally possessing accelerator properties, gl. thor. pr. the first 

 thoracic ganglion. Its two branches communicating with the cervical ganglion 

 surround the subclavian artery forming the annulus of Vieussens. sym. thor. the 

 thoracic sympathetic chain, n, dep. depressor nerve, which, though running by the 

 side of the sympathetic, is really a branch of vagus, from which it separates higher 

 up. This is joined in its course by a branch from the lower cervical ganglion, there 

 being a small ganglion at their junction, from which proceed nerves to form a plexus 

 over the arch of the aorta. It is this branch from the lower cervical ganglion which 

 possesses accelerator properties hence the course of the accelerator fibres is 

 indicated in <the figure by the arrows. 



