54 



THE HEART 



adjacent columns. Cross striation is present, but not to 

 the same degree as in skeletal fibres. The single nucleus 

 is centrally situated. Longitudinal fibres appear not only 

 in the individual cells, but also traversing the partitions 

 between them. 

 The sino-auricular node, 2 mm. in thickness, begins at 



SINO-AUR.ICUbAR. NODE 



AUR.ICUL/^R.-VENTRICUL/^R- 



BUNDLE OF HI5 AND 

 1T5 TWO BRANCHED 



FIBR.E5 OF PURKINJE 



Fig. 9. — Diagrammatic coronal section of the heart to show the 

 junctional tissue. The position of the sino-auricular node is shown 

 on the surface. 



the junction of the superior vena cava and the right auricle, 

 and extends about 2 cm. along the sulcus terminalis. The 

 cells are fusiform, striated, and plentifully surrounded by 

 connective tissue. They are in intimate association with 

 nerve-fibres and nerve-cells, through which connections 

 can be traced with the vagus and sympathetic. 



The auriculo-ventricular junctional tissue begins in the 

 form of fibres from the region of the coronary sinus, and 



