74 THORAX 



round the margin of the orifice. Their apices, margins, 

 and ventricular surfaces are attached to the chordae tendineae. 

 Their auricular surfaces, over which blood flows as it enters 

 the ventricle, are smooth, and their ventricular surfaces are 

 more or less roughened by the attachment of the chordae 

 tendineae, but the roughening is less marked on the ventricular 

 surface of the anterior cusp over which the blood flows as it 

 passes through the conus arteriosus to the pulmonary orifice. 



Pulmonary artery Posterior cusp of pulmonary valve 



Aorta .^^MR^L Supra-ventricular crest 



Pars membranacea septi 



/ Left segment of atrio-ventricular bundle 



Right segment of atrio-ventricular bur 

 ^^ Moderator band 



Base of anterior 

 papillary muscle 



'jjju Fat in sulcus longi 

 Sj^ tudinalis anterior 



Left ventrii 



Coronary sulcus 



Coronary valve 



Opening of coronary sinus | | Medial cusp of tricuspid valve 



Base of medial cusp of tricuspid valve Atrio-ventricular bundle 



FIG. 38. Dissection of the Right Ventricle showing the Atrio- 

 ventricular Bundle. 



The Atrio-ventrictdar 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. 92). To expose this bundle, the anterior part of the medial cusp of the 

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

 When this has been done, the pars membranacea, or upper fibrous part of 

 the inter-ventricular 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 septum, where it divides into right 

 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 pars membranacea 



