252 



PHYSIOLOGY OF THE HEART 



[CH. XXI. 



JugularGanglion 



Ganglion 

 trunci 

 Vagi 



and runs down to the heart within its sheath, forming the joint vago- 

 sympathetic trunk. These fibres are indicated by the dark line in 

 fig. 231. The fibres of the sympathetic seen running up into the 

 skull are for the supply of blood-vessels there. It should be noted 

 that the frog has no spinal accessory nerve. 



In the mammal the sympathetic fibres leave the cord by the 



second and third dorsal 

 nerves, and possibly by an- 

 terior roots of two or more 

 lower nerves ; they pass by 

 the rami communicantes to 

 the ganglion stellatum, or 

 first thoracic ganglion, and 

 thence by the annulus of 

 Vieussens to the inferior 

 cervical ganglion of the sym- 

 pathetic ; fibres from the an- 

 nulus, or from the inferior 

 cervical ganglion, proceed to 

 the heart (see fig. 232). 



In man, the cardiac 

 branches of the sympa- 

 thetic travel to the heart 

 from the annulus of Vieus- 

 sens and cervical sympa- 

 thetic in superior, middle, 

 and lower bundles of fibres. 

 These pass into the cardiac 

 plexus, and surrounding the 

 coronary vessels ultimately 

 reach the heart. 



Inferior Cervical 

 Ganglion 



Subclauian 

 A rtery 



Annulus 



Ganglion Stellatum 



Ant. root 



nd.Thoracic 



Nerue 



~Post.root 



Third 

 Thoracic 

 Ganglion 



PIG. 232. Heart nerves of mammal. (Diagrammatic.) 



By stimulating each rootlet 

 in his three groups, Grossmann 

 found the cardio-inhibitory fibres 

 in the lower two or three rootlets 

 of group b and the upper rootlet 

 of group c. There are probably 

 differences in different animals. 

 In the cat and dog Cadman finds 

 that the rootlets in the a group 



are respiratory and afferent inhibitory, and that all the efferent inhibitory fibres are 

 in group c. 



The inhibitory fibres are medullated, and only measure 2 p to 3 p in diameter ; 

 they pass to the heart and have their cell-stations in the ganglia of that organ. 

 Some of the sympathetic fibres, on the other hand, reach the heart as non- 

 medullated fibres ; having their cell-stations in the sympathetic (inferior cervical 

 and first thoracic) ganglia ; but the majority do not reach their cell-stations until 

 they reach terminal ganglia in the heart wall. The augmentor and accelerator 

 centres in the central nervous system have not yet been accurately localised. 



