184 



THE CIRCULATION OF THE BLOOD 



bifurcates into right and left branches which run down each side of the 

 septum immediately underneath the endocardium. Each main branch 

 ultimately divides up into an intricate system of smaller branches, which 

 become reflected over the inner surface of the ventricles where their exist- 

 ence has been known for some time as the so-called Purkinje fibers. The 

 right bundle remains undivided until after it has run along the moder- 



Fig. 49. Dissection of heart to show auriculoventricular bundle (Keith) ; 3, the beginning of 

 the bundle, known as the A-V node; 2, the bundle dividing into two branches; 4, the branch run- 

 ning on the right side of the interventricular septum. (From Howell's Physiology.) 



Fig. 50. Photograph of model of the auriculoventricular bundle and its ramifications, con- 

 structed from dissections of the heart (Miss De Witt). All of the branches in the left ventricle 

 are not included. (From Howellj 



ator band or its representative, but the left bundle divides early. The 

 fibers ultimately end in close association with the papillary muscles. 

 The node and main bundle and the two branches before they have 

 begun to divide are surrounded by a sheath of fibrous tissue, and 

 they seem to have a liberal blood supply. It is of interest that they con- 

 tain a high percentage of glycogen. In the human heart the auriculo- 



