538 CIRCULATION OF BLOOD AND LYMPH. 



ently. The matter of greatest interest in connection with the dif- 

 ferent chambers has been the nature of the auriculoventricular 

 junction. In the mammalian heart tendinous tissue develops in 

 this region, and for a long time it was supposed that there was no 

 muscular connection between auricles and ventricles. In recent 

 years, however, it has been shown most satisfactorily that there is a 

 peculiar band of cardiac muscle or modified muscle, known usually 

 as the auriculoventricular bundle, which connects auricle and ven- 

 tricle.* 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 



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 Keith). 



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 



* 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. 



fDeWitt, "Anatomical Record," 3, 475, 1909. 



