CHAP, iv.] THE VASCULAR MECHANISM. 255 



r. Vg. roots of the vagus , r.Sp.Ac. roots of the spinal accessory; both drawn 

 very diagrammatically. G.J. ganglion jugulare. G.Tr.Vg. ganglion trunci vagi 

 Sp.Ac. spinal accessory trunk. Ext.Sp.Ac. external spinal accessory. i.Sp.Ac. 

 internal spinal accessory. Vy. trunk of vagus nerve, n.c. branches going to 

 heart C.Sy. cervical sympathetic. G.C. lower cervical ganglion. A.sb. sub- 

 clavian artery. An. V. Annulus of Vieussens. G.St. stellate ganglion, correspond- 

 ing to the first, second, and third ganglia of the thoracic chain. G.Th*, G.Th. 6 , 

 fourth and fifth thoracic ganglia JJ.i., D.u., ZXm., ZXiv., Z).v., first, second, third, 

 fourth and fifth thoracic spinal nerves, r. c. ramus communicans. n. c. nerves 

 (cardiac) passing to the heart from the cervical ganglion and from the annulus of 

 Vieussens. 



The inhibitory fibres, shewn by black lines, run in the upper (bulbar) roots of 

 the spinal accessory, by the internal branch of the spinal accessory, past the 

 ganglion trunci vagi, along the trunk of the vagus, and so by branches to the 

 heart. 



The augmentor fibres, also shewn by black lines, pass from the spinal cord by the 

 anterior roots of the second and third thoracic nerves (possibly also from the "first, 

 fourth and fifth as indicated by broken black lines), pass the stellate ganglion by 

 the annulus of Vieussens to the lower cervical ganglion, from whence, as also from 

 the annulus itself, they pass along the cardiac nerves to the heart. An occasional 

 tract from the stellate ganglion itself is not shewn in the figure. 



slender nerve from the superior cervical ganglion passing independently 

 to the heart. The arrangement is not exactly the same on the two 

 sides of the body, and the minor details differ in different individuals. 

 As in other animals the various cardiac nerves mingle in the cardiac 

 plexuses. 



In the dog it has been ascertained by separate stimulation of 

 these several cardiac nerves, that augmentor fibres are contained in 

 some or other of the nerves passing from the lower cervical ganglion 

 and the adjoining vagus trunk, from the annulus of Vieussens, 

 especially the lower, ventral, limb, and sometimes from the stellate 

 ganglion itself. The results differ a good deal in different in- 

 dividuals, and there are reasons for thinking that the nerves in 

 question may contain efferent fibres other than augmentor fibres, 

 by reason of which stimulation of them may give rise to other 

 than pure augmentor effects. Speaking broadly, however, we may 

 say that we may trace the augmentor fibres back from the cardiac 

 plexuses through the lower cervical ganglion and the annulus of 

 Vienssens to the stellate ganglion. 



This ganglion is in reality several sympathetic ganglia fused 

 together. It undoubtedly, in the dog, represents the first, second 

 and third thoracic sympathetic ganglia, receiving, as it does, 

 branches, rami communicantes, from the first, second and third 

 thoracic spinal nerves. Since it also receives branches from the 

 eighth and seventh cervical nerves, it has been argued that it 

 represents not only the three thoracic sympathetic ganglia, but 

 also what in man and other animals is called the lower cervical 

 ganglion ; if so, what has been called above the lower cervical 

 ganglion should be regarded as the middle cervical ganglion. 

 From the stellate ganglion the sympathetic cord passes to the 

 ganglion, which is connected by a ramus communicans with the 



