THE HEART 



41 



reveal this division of the bundle as a delicate flattened ribbon 

 of fibres passing downward directly beneath the endocardium. 

 The ribbon soon breaks up into smaller strands which pass to the 

 musculi papillares situated on the septum (4, 6, Fig. 3). 



Arising from the groups of niusculi papillares in either chamber 

 are the terminal ramifications of the bundle. They frequently, 

 especially on the right side, take the form of small moderator 

 bands, and pass out to all parts of the ventricular wall. Here 



FIG. 2. Right auricle and ventricle of calf (Keith). 1, Central cartilage ; 

 2, main bundle ; 3, A-V node ; 4, right septal division ; 5, moderator band ; 

 8, orifice of coronary sinus. 



they can be seen as delicate trabeculse passing from one part to 

 another. Eventually they fuse with the ventricular musculature. 



With regard to the microscopic appearances of the various 

 parts of the bundle, Tawara in his book gives drawings of them for 

 the sheep's heart. In such hearts they are quite easy to recognise. 

 The chief points to be noted are (1) The peculiar branched cells of 

 the A-V node. (2) The large pale cells of the main bundle with 

 their large nuclei. (3) The peculiar Purkinje cells found in the 

 septal divisions, and their terminal ramifications (especially in a so- 

 called moderator band). 



