148 



A MANUAL OF PHYSIOLOGY . 



In the dog the vagus and cervical sympathetic are, in the great 

 majority of cases, contained in a strong common sheath, and pass 

 together through the inferior cervical ganglion. Upon opening this 

 sheath they may with care be separated, the fibres running in dis- 

 tinct strands, and not mixed together as in the vago-sympathetic 

 of the frog. For some distance below the superior cervical ganglion 

 the cervical sympathetic is not connected with the vagus, and here 

 the nerves may be separately stimulated without any artificial 



isolation, but the electrodes must be 

 very well insulated, as the available 

 length of nerve is small. 



In the rabbit and some other mam- 

 mals, including man, the vagus and 

 sympathetic run a separate course in 

 the neck. 



GTV- 



\n 



The effects of stimulation of the 

 vagus or vago-sympathetic in the 

 mammal are very much the same as 

 in the frog, except that secondary 

 augmentation is in general less 

 marked, though often present in 

 some degree, and that in the mammal 

 the inhibitory fibres have a smaller 

 direct action on the ventricle. It 

 indeed beats more slowly when the 

 auricle is slowed, but this is only 

 because in the normally beating 

 heart the ventricle takes the time 

 from the auricle. The strength of 

 the ventricular contractions may be 

 not at all diminished, even when the 

 auricle is beating very feebly during 

 inhibition. When the auricle is com- 

 pletely stopped, which does not occur 

 so readily as in the frog, the ventricle 

 also stops for a short time, but soon 

 begins to beat again with an inde- 

 pendent rhythm of its own. In the 

 frog the ventricle is directly affected 

 by stimulation of the vagus, and the 

 force of its beats is diminished inde- 

 pendently of the inhibitory effects in the [auricles (Practical 

 Exercises, pp. 182, 187). 



The inhibitory fibres, then, influence the heart particularly 

 through the auricles ; they are par excellence auricular nerves. 

 On the other hand, the accelerantes in all mammals which have 

 been investigated not only extend to the ventricles, but are 

 even mainly distributed to them. They are emphatically ven- 



m 



FIG. 62. DIAGRAM OF CARDIAC 

 NERVES IN THE DOG (AFTER 

 FOSTER). 



II, III, second and third dor- 

 sal nerves ; SA, subclavian ar- 

 tery ; AV, annulus of Vieussens ; 

 ICG, inferior cervical ganglion ; 

 CS, cervical sympathetic ; i, first 

 thoracic or stellate ganglion 

 of the sympathetic ; 2, second 

 thoracic ganglion ; Ac., accele- 

 rator or augmentor fibres pass- 

 ing off towards the heart ; X, 

 roots of vagus ; XI, roots of 

 spinal accessory ; JG, jugular 

 ganglion ; GTV, ganglion trunci 

 vagi ; In., inhibitory fibres pass- 

 ing off towards the heart. 



