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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.
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.
RECORD.-VOL. 111, No. 12.
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.
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