THE CIRCULATION OF THE BLOOD AND LYMPH 



139 



GTV 



In mammals (and in what follows we shall restrict ourselves to the 

 dog, cat and rabbit, as it is in these animals that the subject has been 

 chiefly studied) the inhibitory fibres run down the vagus in the neck 

 and reach the heart by its cardiac branches. They are not, however, 

 generally believed to be derived from the roots of the vagus itself, but 

 from the inner branch of the spinal accessory, which joins the vagus. 

 The augmentor fibres leave the spinal cord in the anterior roots of the 

 second and third thoracic nerves, and 

 possibly to some extent by the fourth 

 and fifth. Through the corresponding 

 white rami communicantes they reach 

 the sympathetic cord, and running 

 up through the stellate ganglion (first 

 thoracic), and the armulus of Vieussens, 

 which surrounds the subclavian artery, 

 to the inferior cervical ganglion, they 

 pass off to the heart by separate * ac- 

 celerator ' branches, taking origin either 

 from the annulus or from the inferior 

 cervical ganglion. 



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. After open- 

 ing this sheath they may with care be 

 separated, the fibres running in distinct 

 strands, and not mixed together as in 

 the vago-sympathetic of the frog. For 

 some distance below the superior 

 cervical ganglion the cervical sympa- 

 thetic is not connected with the vagus, 

 and here the nerves may be separately 

 stimulated without any artificial isola- 

 tion, but the electrodes must be very 

 well insulated, as the available length 

 of nerve is small. 



In the rabbit, cat, horse, and some 

 other mammals, the vagus and sympa- 

 thetic run a separate course in the 

 neck. 



II 



in 



FIG. 50. DIAGRAM OF CAR- 

 DIAC NERVES IN THE DOG 

 (AFTER FOSTER). 



II, III, second and third dorsal 

 nerves ; SA, subclavian artery ; 

 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., accelerator or 

 augmentor fibres passing off to- 

 wards the heart ; X, roots of vagus ; 

 XI, roots of spinal accessory ; JG, 

 jugular ganglion ; GTV, ganglion 

 trunci vagi ; In., inhibitory fibres 

 passing off towards the heart. 



The effects of stimulation of the vagus or vago-sym- 

 pathetic in the mammal are very much the same as in the 

 frog, except that secondary augmentation is far less marked 

 or altogether absent, and that in the mammal the inhibitory 

 fibres have no direct action on the ventricle. It indeed 

 beats more slowly when the auricle is slowed, but this is 



