184 THE CIRCULATION OF THE BLOOD 



valve, it bifurcates so as to send a branch down each side of the septum 

 immediately below the endocardium. Each main branch, as it proceeds 

 downward on the septum, divides up into an intricate system of smaller 

 branches, which become reflected over the inner surface of the ventricles, 

 where their existence has been known for some time as the so-called 



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 Ho well'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 Howell.) 



Purkinje filters. 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 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- 



