THORACIC CAVITY 



101 



The Atrio-ventricular Bundle. The atrio- ventricular bundle is a small 

 bundle of peculiar muscle fibres, of pale colour, which forms the only direct 

 muscular connection between the walls of the atria and the ventricles (see 

 p. 121). To expose it, the anterior part of the medial cusp of the tricuspid 

 valve must be detached from the fibrous atrio-ventricular ring. When 

 that has been done, the membranous upper part of the interventricular 

 septum will be exposed, and the atrio-ventricular bundle will be found 

 running along its posterior and lower border to the upper end of the 

 muscular part of the interventricular septum, where it divides into right 



Pulmonary artery 

 Aorta 



Posterior cusp of pulmonary valve 



J0J Supra-ventricular crest 



/ Pars membranacea septi 



\ight auricle 



Left segment of atrio-ventricular bundle 

 



Right segment of atrio-ventricular bundle 



Moderator band 



Base of anterior 

 papillary muscle 



Fat in anterior longi- 

 tudinal sulcus 



Left ventricle 



Coronary sulcus / 



Coronary valve 



Opening of coronary sinus | 



Base of medial cusp of tricuspid valve 



| Medial cusp of tricuspid valve 



Atrio-ventricular bundle 



FIG. 51. Dissection of the Right Ventricle showing the Atrio- 

 ventricular Bundle. 



and left branches. The right branch runs along the right side of the 

 septum to the moderator band, along which it passes to the anterior 

 papillary muscle. The left branch passes between the membranous part 

 and the upper end of the muscular part of the septum, and then descends 

 along the left side of the septum. Both branches send off numerous rami- 

 fications which are distributed to the various parts of the walls of the 

 ventricles. It is only occasionally that the atrio-ventricular bundle can be 

 displayed in the heart of an ordinary dissecting-room subject. 



The pulmonary orifice lies at the upper, posterior, and left 

 part of the ventricle, at the apex of the conus arteriosus. Its 

 centre is behind the third left costal cartilage immediately to 

 n76 



