95 



Fig. 2. This is a part of the right auricle and the interventricular 

 septum, as seen from the right ventricle of the heart from which 

 Fig. 1 is drawn. Here a nodule of muscle grows up from the inter- 

 ventricular septum and invades the pars membranacea septi, making 

 it very narrow. From the reticulum the main bundle can be seen for 

 3 or 4 mm and it disappears between the central fibrous body and 

 the septal muscle. At this point there is a well-marked bursa which 

 does not show well in the drawing. The main bundle divides on the 

 other side of the septum and the right septal branch, as indicated by 

 the index line, appears on the right side, just after the division. It 

 could be seen distinctly through the endocardium, but in the dissection 

 this has been removed. The right septal branch then disappears 

 into the papillary muscle, which in this case is continuous with the 

 moderator band. 



Other points in the drawing are explained by the index lines. 



Fig. 3 is a photograph of a dissection of the reticulum with its 

 chief auricular branches and the auriculo-bundle as seen from the 

 right side of a calf's heart. The external walls of the right auricle 

 and ventricle are removed. The interauricular septum in the region 

 of the reticulum is made up of the septal wall of the right auricle 

 lying against the septal wall of the left auricle, holding between 

 them — as between two leaves of a book — the reticulum and the 

 beginning of its branches. In order to see these, the right auricular 

 part of the septal wall must be removed, as shown in the photograph, 

 and on careful dissection the reticulum will appear as a mass somewhat 

 resembling a ganglion in form. The right auricle is cut away suf- 

 ficiently to show the branch going to the left auricle with its distri- 

 bution to the coronary sinus, under which its course Kes as it proceeds 

 in the direction of the auricular appendix and mouths of the pulmo- 

 nary veins. The large branch which goes to the right auricular 

 appendix is pinned down to the cut edge of the right ventricular wall. 

 The trunk of the branches to the interauricular septum and the superior 

 cava is dissected out for a short distance, sufficient to show its direction. 

 Fibres going into the septal cusp and right ventricle immediately before 

 the auriculo- ventricular bundle is given off, are also well shown in the 

 photograph. Behind this pinkish pale mass (the reticulum and its 

 branches) can be seen the darker muscle of the left auricle some 

 strands of which are inserted into the auriculo-ventricular fibrous ring 

 and some into the central cartilage. A well-marked band of dark 

 auricular muscle arising partly from the annular ring of the inferior 

 cava and also from the left auricle, can be seen disappearing between 



