NERVOUS CONTROL OF THE CIRCULATION 



177 



been called tlie intrinsic nerves of the heart, which were 

 formerly treated as independent of the other two sets 

 of nerve fibers. The intrin- 

 sic nerves are now known, 

 however, to be merely the 

 terminations of the other 

 nerves in the heart wall, 

 while the rhythmic beat of 

 the ventricles, which is 

 found to continue for some 

 time even after the heart 

 is removed from the body, 

 is believed to be a peculiar 

 property of the heart muscle 

 itself. 



242. Path of the Nervous 

 Impulse. The roots of the 

 vagus and the spinal acces- 

 sory nerves rise near together /, kgp^ 



in the gray matter of the 



medulla oblongata. A branch Fig. 99. Diagram illustrating the 

 from the spinal accessory 

 soon joins the vagus, and 

 supplies some of its motor 

 or efferent fibers. Fibers 

 from the sympathetic nerves 

 of the neck also join the va- 

 gus. These have been traced 

 back into the spinal cord. 

 The cardiac nerves, there- 

 fore, are all connected with 

 the central nervous system, 

 and, since all parts of the 



nervous control of the heart. 



A cardiac accelerator center. 



a accelerator fibers connected with 

 accelerator center through sym- 

 pathetic system (Sy), spinal 

 nerves (<S) , and spinal cord. 



c fibers through which the cerebrum 

 exercises control over the car- 

 diac centers. 



e fibers from the heart that excite 

 the inhibitory center. 



I cardiac inhibitory center. 



i inhibitory fibers whose action 

 slows the heart's beating. 



s communicating fibers between 

 spinal nerves and sympathetic 

 system. 



Sy sympathetic system. 



