HEAET 



199 



These muscular columns may present any one of three modes of 

 attachment to the myocardium : ( 1 ) they may be attached along their 

 entire extent; (2) they may be attached only at their two ends, the mid- 

 portion being free; (3) they may be attached to the myocardium at one 

 end only, the other end projecting into the ventricular cavity as a papil- 

 lary muscle, from whose apex chordae tendineas pass to the auriculoven- 



Coronary Sinus 

 Reticulum 



Main Bundle of Hi, 

 Pulmonary Veins 



Sup. Cava 



Aorta 



Pulmonary Artery 



( Muscular Fibers Streaming to 

 \ the Reticulum 

 Right Auricle 



Pars Mem. Septi 

 5 BifurcationofMainBundleinto 

 1 Right and Left Sept. Branches 

 Right Septal Branch 



Moderator Band 



Artery to Bundle 



Tricuspid \/ ahe 



Right Ventricle 



Chordce Tendineas 



Papillary Muscle 



FIG. 215. HUMAN HEART OPENED FROM THE RIGHT TO SHOW THE ATRIOVEN- 

 TRICULAR BUNDLE OF His. 



The illustration shows also a heart valve, the chordae tendinese, and the pap- 

 illary muscles. (After Curran, Anat. Rec., 3, 12, 1909.) 



tricular valves. Either of the last two forms may, in transections of the 

 ventricles, appear as isolated islands of muscular tissue surrounded by 

 endocardium and lying apparently free within the cavity of the ventricle. 

 Columnar carnese which span the ventricular cavity constitute moderator 

 bands. One such band is frequently present in the right ventricle near the 

 apex, and occasionally one appears in the left ventricle. 



Atrioventricular Bundle. The atrioventricular bundle of His was 

 discovered in the human heart by His, Jr., in 1893. Previously in the 

 same year it had been noted by Kent in the heart of a number of mam- 

 mals. It has since been seen in every species of mammal investigated, 



