206 



THE VASCULAR MECHANISM. 



O.Tr.Vg.- 



Vg _ 



annulus of Vieussens, passing along one or other or both loops, to the inferior 

 cervical ganglion. Their further course to the heart is along the nerves 



springing either from the inferior cer- 



FIG. 76. vical ganglion or from the loop of 



Vieussens directly. Their exact path 

 from the ganglia in fact seems to vary 

 in different individuals. 



The path of the augmentor fibres 

 has not been worked out so fully in 

 other mammals as in the dog, but it 

 \ r.Sp.Ac.' ls most probable that in all cases they 

 leave the spinal cord by the anterior 

 roots of the second and third dorsal 

 nerves (possibly also by the fourth 

 and fifth) and, passing up the sympa- 

 thetic chain to the ganglion stellatum 

 and annulus of Vieussens, proceed to 

 the heart by nerves branching off 

 from some part or other of the annu- 

 lus or from the lower and middla 

 cervical ganglia. 



Diagrammatic Representation of the Cardial 

 Inhibitory and Augmentor Fibres in the Dog. 

 The upper portion of the figure represents the 

 inhibitory, the lower the augmentor fibres. 

 r.Vg., roots of the vagus; r.Sp.Ac., roots of the 

 spinal accessory ; both drawn very diagram- 

 matically. 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 ; V(j., trunk 

 of vagus nerve; n.c., branches going to heart; 

 C.Sy., cervical sympathetic; O.C., lower cervi- 

 cal ganglion: A.sb., subclavian artery; An. V., 

 annulus of Vieussens; G.St.(Th. 1 ), ganglion 

 stellatum or first thoracic ganglion; G.Th.*, 

 G.Th 3 , G.Th*, second, third, and fourth tho- 

 racic ganglia ; D.IL, D.III., D.IV., D.V., second 

 third, fourth, and fifth thoracic spinal nerves ; 

 r.c., ramus communicans ; n.c., nerves (car- 

 diac) passing to heart (superior vena cava) from 

 cervical ganglion and from the annulus of 

 Vieussens. 



The inhibitory fibres, shown by black line, 

 run in the upper (medullary 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 superior vena cava and the heart. 



The augmentor fibres, also shown by black 

 line, pass from the spinal cord by the anterior 

 roots of the second and third thoracic nerves 

 (possibly also from fourth and fifth as indicated 

 by broken black line), pass the second and first 

 (stellate) thoracic ganglia 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 superior 

 vena cava. 



The effects of stimulating these augmentor fibres in the mammal are, in 

 general, the same as those witnessed in the frog. In the mammal, as in the 

 frog, impulses along these augmentor fibres may be originated in the central 



