FIQ.1.-This is a drawing of a human heart opened from the right side, showing the right auricle and the rlght ventricular surface of the interventricular septum. The great vessels are somewhat diagrammatic, a s they mere not saved in a suitable state for a clear drawing. The auriculo-ventricular bundle is large-being 3 mm. in width all along its course from the central fibrous body to its bifurcation. The central fibrous body is represented in blnck just to the left of the index line to the main bundle and on the auriculhr side. The auricular fibres of the system are shown streaming from the superior cava, the annular muscle around the fossa ovalis, t h e right auricular ring and t h e cusps. The septal artery, which gives small twigs to the reticulum and to the bundle, is also shown. The bundle is dissected at the point of bifurcation, to show the beginning of the left septal branch. The right septal branch is dissected as f a r as possible into the moderator band. The index lines explain sufficiently well the other landmarks In the disscction. FIG.2.-This is a drawing of a human heart opeued from the left side to show the left septa1 branch of the auriculo-ventricular bundle streaming down the interventricular septum. In this case no attempt was made to dissect it out, because it showed clearly as represented through the normal endocardium. It is always quite superficial on this side, although in a thickened endocardium it cannot usually be seen so well in the human heart. The spaces under the endocardium here can be blown up from the bursa of the main bundle. Notice the relationships of the non-coronary cusp, pars membranacea septl, and the base of the mitral vnlve to the course of the flbres of the auriculo-ventricular system. FIG. 3.-This is a drawing of the region around the auriculo-ventricular bundle as seen from the right side. F is position of central fibrous body where the main bundle begins to leave the auricle. H, fossa ovalis. 8,coronary sinus. C, auricular appendix. E , a cut through endocardium, over the main bundle, showing the latter lying in the bursal groove or canal, and the bursal space emphasized by a pull on the threads A and B which are put through the endocardium for this purpose. D, a hollow ridge along the course of the main bundle, caused by the pull on the thread B. FIG. 4.-Fig. 4 is a drawing of the subaortic region in the left ventricle, showing the bursa on this side. This is a common variation from the normal, and it occurs when the subaortic musculature comes up high, invading the pars membranacea septi. It is the left side of the heart from which Fig. 5 was drawn. The subaortic musculature, as drawn in Fig. 4, shows some of the various directions which the fibres of this may take. I n this dissection the left septal branch first appears below the transverse fibres, about the end of the index line marked “Left Ventricle,” but they have lost their color and do not show in the drawing. The bursal space is held out by a thread inserted for the purpose, and the main bundle is seen lying at the bottom of it. FIQ.5.-This is a part of the right auricle and the interventricular septum, as seen from the right ventricle of the heart from which Fig. 4 is drawn. Here a nodule of muscle grows up from the interventricular 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 wellmarked 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 septnl branch then disappears into the papillary muscle, which is sometimes continuous with the moderator band. Other points in the drawing are explained by the index lines. THE BUNDLE OF HIS. 1. J . CLJIIRAN. TIIB ANATOUICAL RECOI~D.-VOL.111, No. 12. PLATE I1 FIG.6.-Fig. 6 is from a photograph of a dissection of the reticulum with its chief auricular branches and the auriculo-ventricular bundle as seen from the right side of a calf’s heart. The external walls of the right auricle and ventricle are removed. The 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, t h e 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 sufaciently to show the branch going to the left auricle with its distribution to the coronary sinus, under which its course lies as it proceeds in the direction of the auricular appendix and mouths of the pulmonary 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, sufiicient 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 a r e 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 the fossa ovalis and the left auricular branch of the reticulum, under the septal branch, and again appearing in the small triangular area, as it is inserted into the central cartilage of the heart. These and other points are indicated in Fig. 7, which is a key to this photograph. THE BUNDLE O F HIS. E. J. CURIIAN. THI ANATOMICAL RECORD.-VOL. 111, No. 12. PLATE III. Fro. ’i.-Key to Fig. 6. A, inferior cava turned up. B, septal branch of left coronary artery, which sends twigs to the reticulum and the auriculoventricular bundle. 0,reticulum. D, fibres from the reticulum to ventricle and septal cusp. E, insertion of muscular band H, arising from left auricle and inferior cava. F ,superior cava. (f, Fossa ovalis. I, left auricular branch of reticulum going to mouths of pulmonary veins, auricular appendix, and coronary sinus. J, coronary sinus. K, branch of reticulum going to right auricular appendix, now pinned to the cut wall of the right ventricle. L, left ventricle. M , right auricle. N, branch from the reticulum to the interauricular septum and mouth of superior cava. 0,central flbrous cartilage. P , a twig of right septal branch to conus arteriosus of right ventricle, given off before the remaining part enters the moderator band. 8 , interventricular septum seen from right ventricle. Fro. 8.-Fig. 8 is a drawing of a dissection of a sheep’s heart, showing a view of the auricular connections of the auriculo-ventricular bundle similar to that shown by the photograph (Fig. 6). I n this case the coronary sinus is dissected away and the left auricular branch, E, of the reticulum is shown at first as a wide band which, when it proceeds but a little distance, buries itself deeply in the left auricular musculature, only a fine strand of it showing on the surface for any considerable distance. A, trunk of left pulmonary veins. B, trunk of right pulmonary veins. C,left auricular appendix. D , fossa ovalis. E, left auricular branch of reticulum. F, septal branch of reticulum. (f, reticulum. H, right auricular branch of the reticulum on its way to the auricular appendix. I, cut edge of the left ventricle. J , left ventricle. K , main auriculo-ventricular bundle. L, superior cava. M , right auricular appendix. N, right auricle. 0, bifurcation of main bundle. P, right septal branch. &, moderator band cut. R, right ventricle, septal wall. The accessory ventricular branch is also seen well in this direction. T H E BUNDLE OF FIB. 1. J. CURRAN. Tnla ANATOMICALRECOXD.-VOL. 111, No. 12, PLATE m.