468 
DR. PETTIGREW ON THE ARRANGEMENT OE THE FIBRES 
fig. 18) run in a spiral almost vertical direction* from left to right downwards, some of 
them proceeding to the left apex ( d "), others to the right ventricle (f) ; and if an inci- 
sion be made through the right ventricular wall (Plate XIII. fig. 19), a little to the 
right of the posterior coronary track, and the breach dilated to expose the septum and 
the interior of the right ventricle, it will be seen that the fibres on the right side of the 
septum (g) follow a similar course. On the anterior aspect of the ventricles (Plate XIII. 
fig. 20) the fibres also pursue a spiral nearly vertical direction from left to right down- 
wards f; but there is a great difference between them and the fibres on the posterior 
aspect. 
On the posterior of the ventricles (Plate XIII. fig. 18) the fibres from the left 
auriculo-ventricular opening and the left ventricle generally (df) cross the track for 
the posterior coronary artery (j), and are found also on the right ventricle ( f'f 
hence the epithet common fibres ; whereas on the anterior of the ventricles (Plate XIII. 
fig. 20) the fibres, with the exception of the cross band at the base already referred 
to ( n ), dip in at the anterior coronary track (o), to appear on the right third of the 
septum (Plate XIII. fig. 19, g , A), where they are continuous with fibres having a corre- 
sponding direction. The fibres occurring on the right side of the septum (Plate XIII. 
fig. 19 ,g,h), as well as those lining the interior of the right ventricle generally, are, 
for anything I can discover to the contrary, segmental portions lopped off or isolated 
by the primary notch or reduplication (Plate XVI. diag. 15, A ; Plate XV. compare k l 
with mn of fig. 45) from the spiral nearly vertical fibres originally lining the interior of 
the left or typical ventricle. If this explanation be adopted, the great structural resem- 
blance presented by the internal fibres of the right and left ventricles respectively is at 
once accounted for. 
Septum Ventriculorum composed of two elements {Mammal). That two elements enter 
into the composition of the septum is probable for the following reasons : — 
1st. If the right ventricle be detached a little to the right of the tracks for the ante- 
rior and posterior coronary arteries, and the septum dissected from the right side (Plate 
XII. figs. 1, 2, 3, & 4), many of the fibres {g e ) at no great depth from the surface proceed 
without breach of continuity to the anterior wall (Plate XII. fig. 10, f) and apex (g) of 
the left ventricle, thus showing that they belong exclusively to the left ventricle ; whereas 
a certain number of them, as has been stated, are ascertained to be continuous with the 
fibres on the outside of the right ventricular wall (Plate XIII. fig. 21, ff"), proving 
them to belong more particularly to the right ventricle. 
* The superficial fibres from the right and left ventricles converge in the track for the posterior coronary 
artery in a manner resembling the letter V ( ff'j ) — an arrangement which is confined to the upper or basal 
third of the first layer. Ultimately these fibres curve round to enter the left apex anteriorly. 
f In the superficial layers of the right ventricle anteriorly, the fibres at the root of the pulmonary artery 
interweave to a considerable extent, and are matted together. As a similar arrangement exists in the super- 
ficial layers of the left ventricle at the root of the aorta, it is just possible that the large vessels are thereby 
supplied with more secure points of attachment. 
