994 



PHYSIOLOGY 



of the coronary sinus. From this point a bundle of muscular fibres (the 

 bundle of His or the auriculo-ventricular or A.V. bundle) runs along the top 

 of the interventricular septum just below its membranous part and then 

 divides into the right and left septal divisions, which pass down in each ven- 

 tricle on the. interventricular septum into the papillary muscle arising from 

 the septum. Each half of the bundle gives off several branches which break 

 up more and more, finally forming a reticulated sheet of tissue over the 

 greater * part of the interior of the ventricles just below the endocardium. 

 The fibres composing this tissue are more primitive in character than the 

 rest of the cardiac musculature and have long been distinguished as the 



Superior Vena Garal.. 



Sin&auricular 



-AORTA 



^Appendix. 



'uscle 



Fits. 440. Diagrammatic representation of course of A.V. bundle. 



' fibres of Purkinje.' In them the fibrillation is confined to the periphery of 

 the muscle cell. They are distinguished by a high glycogen content. They 

 may be regarded as a part of the muscular wall of the heart specially differen- 

 tiated for the rapid conduction of the excitatory process to all parts of the 

 ventricles (Figs. 441 and 442). 



Numerous nerve fibres and gangb'on cells are foundPto accompany the muscle fibres 

 of the auriculo-ventricular bundle. We have however no reasons for regarding the 

 nervous structures as concerned in the propagation of the excitatory wave. 



The auriculo-ventricular bundle forms the only continuous muscular 

 tissue between the auricles and ventricles, and destruction of it causes com- 

 plete abolition of the normal sequence of beat between auricles and ventricles. 

 By leading off different parts of the heart to the string galvanometer, it is 

 possible to determine the time relations of the excitatory process. It is 

 then found that the mass of Purkinje tissue, known as the sino-auricular 



