IN THE VENTRICLES OE THE VERTEBRATE HEART. 
469 
2ndly. The fibres of the right side of the septum, especially the right third of it, are 
densely matted together, and separate with greater difficulty than the fibres of the other 
portions of the septum and ventricular wall generally. 
3rdly. The exact width of the septum (Plate XV. fig. 50, c' d'), as compared with the 
left ventricular wall (c d) between the musculi papillares {x, y), is in some parts nearly 
one-third greater — this increase in bulk affording a redundancy of material, which was 
to be anticipated, since the two halves of the septal fold (Plate XVI. diagram 16, H K) 
are supposed to have passed partially through, and become blended with each other 
(Plate XVI. diagram 17, E J). 
4thly. Such of the fibres as are found near the centre of the right third of the septum 
cross each other slightly towards the base, and give rise to a curious Y-shaped arrange- 
ment at a point corresponding to the crossing which would be produced by the redupli- 
cation. 
There are other arguments in favour of the septum being formed of two elements by 
a septal reduplication. 
When, for example, the common fibres are dissected posteriorly, more or less inter- 
ruption is experienced in their separation (particularly in the deeper layers) in a line 
corresponding with the track of the posterior coronary artery (Plate XV. fig. 54, c </), 
where the fibres of the border of the reduplication (Plate XYI. diagram 16, G) are 
believed to have united with the fibres of the posterior wall (B). 
The external fibres of the right ventricular wall moreover (Plate XIII. fig. 20, d'f, 
and fig. 23, p g) enter the track for the anterior coronary artery (o) throughout its entire 
extent, for the purpose of appearing on the septum (Plate XIII. figs. 19 & 22, g), the 
track referred to corresponding with the rut which would be produced by the junction 
of the two halves of the septal duplicature (Plate XYI. diagram 16, A). 
Lastly, the external fibres of the right ventricular wall enter the interior by simply 
bending or folding upon themselves (Plate XIY. figs. 34&35, de,fg, and Plate XY. 
fig. 45, Jc, o, l) — an arrangement which presupposes a corresponding reduplication or 
folding in of the anterior wall at some period or other, and one which is altogether 
different from the arrangement of the external fibres of the left ventricle at the apex, 
where the fibres enter the interior in two divisions in a regular whorl (Plate XII. fig. 10, 
g , d, and Plate XYI. fig. 55, e,f). 
Cameos columns and musculi papillares of the right ventricle {Mammal). The carneee 
columnse of the right ventricle (Plate XIY. figs. 43 & 44) are in general better marked, 
and the musculi papillares more numerous than in the left — a modification traceable 
partly to the shape of the right ventricular cavity (Plate XV. fig. 49, l), and partly to 
the greater number of fixed points required for the attachments of the chordae tendineee 
distributed to the tricuspid valve. 
In the right ventricle, as in the left, the carnese columnse pursue a spiral nearly vertical 
direction from right to left upwards, and are subject to great variation as regards size, 
number, and general appearance. The musculi papillares in this ventricle, although 
mdccclxiv. 3 R 
