542 CIRCULATION OF BLOOD AND LYMPH. 



ventricle.* The bundle as a definite structure begins at the base of 

 the interauricular septum, at the posterior margin, and on the 

 right side in a collection of small cells or fibers known as the node, 

 or the auriculoventricular node (A-V node), it runs as a bundle along 

 the top of the interventricular septum (see Fig. 225), and near the 

 union of the posterior and median flaps of the aortic valve it 

 divides into two main branches, one of which enters the right 

 ventricle, the other the left, each lying beneath the endocardium. 

 Passing^ down the septal wall, these branches divide, f as repre- 

 sented in Fig. 226, to form a system of strands that can be traced 

 over the inner surface of the ventricles, constituting what were 



Fig. 225. To show the position of the auriculoventricular bundle in the heart of the calf: 

 2, The auriculoventricular bundle. As it runs along the top of the ventricular septum, it is 

 seen to divide into two branches, one entering the right, the other the left, ventricle; 3, the begin- 

 ning of the bundle in the auricular septum known as the A-V node; 4, the branch of the bundle 

 entering the right ventricle in the septal wall; 1, central cartilage (from Keith). 



formerly designated as Purkinje fibers. The auriculoventricular 

 node in the interauricular septum is connected with the muscula- 

 ture of the auricles, and through muscle bundles in the septum with 

 the remnant of sinus tissue (sino-auricular node) at the mouth of 

 the superior vena cava. The main bundle and the larger branches 

 of this system are surrounded by fibrous tissue, and it is uncer- 

 tain whether or not they actually contract during the beat of the 



* See Retzer, " Archiv f. Anatomic," 1904, p. 1, and "Anatomical Record," 

 2, 149, 1908; Braeunig, "Archiv f. Physiologic," 1904, suppl. volume, p. 1; 

 Tawara, "Das Reizleitungssystem des Saugethierherzens," Jena, 1906. 



t DeWitt, "Anatomical Record," 3, 475, 1909. 



