THE HEART BEAT. 



535 



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 network of interlacing fibers known as the node, 

 or the auriculoventricular 7wde (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 endo- 

 cardium. Passing down the septal wall, these branches divide,! 

 as represented in Fig. 22G, to form a system of strands that can be 

 traced over the inner surface of the ventricles beneath the endo- 



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 ia 

 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 Ke^fh). 



cardium, constituting what were formerly designated as Purkinje 

 fibers. The main bundle and the larger branches of this system 

 are surrounded by fibrous tissue, and it is uncertain whether or 

 not they actually contract during the beat of the heart, but there 

 is little doubt that they constitute a conducting system of modified 

 muscular tissue through which the excitation is conveyed from the 

 auriculoventricular node to the ventricular musculature. The con- 



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

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

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



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



