42 



THE HEART 



In the human heart the different portions of the bundle are not 

 so easy to recognise microscopically. With a little practice, however, 

 the bundle can be traced through a series of sections in its course 



FIG. 3. Left ventricle of calf (Keith). 1, Left septal division of A-V bundle ; 

 2, 3, subaortic musculature divided to show passage of bundle from right side of 

 heart; 4, 5, branches of left septal division ; 6, free muscular "moderator" bands 

 containing prolongations of bundle ; 9, left auricle ; 10, aorta ; 13, pulmonary 

 artery. 



from auricle to ventricle. It will be found that the node is made 

 up of closely interwoven fibres and a certain amount of fibrous 

 tissue. The main bundle is completely separated from the re- 

 maining musculature by fibrous tissue, and is made up of paler 



