486 
DR. PETTIGREW ON THE ARRANGEMENT OE THE FIBRES 
and which when the sheet is rolled up represents two deeper layers (Plate XVI. diagram 
3, F G H I J), be taken, it will be found to pursue a similar though slightly more oblique 
course, and to extend from the extreme base (F) to a point somewhat short of the 
extreme apex (H), where it turns abruptly upon itself at a much wider part of the cone, 
to change its direction and enter the interior ; after which, like the other, it gradually 
regains the base (J), — an arrangement which proves that the apex of the artifical cone 
or ventricle is opened into or enlarged by the removal of successive lines, precisely in 
the same way that the apex of the left ventricle is opened into, or enlarged, by the 
removal of successive layers (Plate XII. compare fg, e d, of fig. 9 with kl of fig. 11). 
It further shows that many of the lines, like the fibres themselves, return to points not 
wide of those from which they started. If another line, about the middle of the sheet 
(Plates XV. & XVI. diagrams 1 & 3, K L M N O), be taken, and traced in the same 
manner, it will be seen to proceed from the extreme base K (Plate XII. compare with 
fibres marked f in fig. 3), and to turn upon itself or reverse its direction and enter the 
interior at a still wider portion of the cone M (Plate XII. compare with fibres marked 
Jc in fig. 3) — i. e. at a point still further removed from the original apex (C) — and so on 
until the opposite marginal line (Plates XV. & XVI. diagrams 1 & 3, UVW) is reached, 
which confines itself entirely to the base, or upper portion of the cone (Plate XII. 
compare with fibres marked fg, d! e, fig. 4), and makes only one turn of a spiral. This 
disposition of the lines reveals what to me is a very interesting fact, viz. that certain 
lines, like certain layers, are confined to certain localities or regions. (The first layer 
of the left ventricle, as was pointed out, extends from the extreme base to the extreme 
apex (Plate XII. fig. 1), while the fourth layer does not quite extend to either (Plate 
XII. fig. 4). It further shows, what is scarcely less important, that, of the lines origin- 
ally of the same length, some, from the fact of their winding very partially round the 
base or wider portion of the 'cone (Plate XVI. diagram 3, A) while they twist rapidly 
round the apex or narrow part (B C), make one turn and a half of a spiral, whereas 
others, which are confined to and wind round the base or wider portion of the cone, 
make only one turn of a spiral (Plate XVI. diagram 3, U V W) — an arrangement which, 
as I endeavoured to point out (see p. 456), prevails also in the left ventricle. When the 
interior of the cone, fashioned as recommended, is examined, the marginal lines are 
observed to twist out of the apex (Plate XVI. diagram 9, Y) and assume a more or less 
vertical direction (Plate XVI. diagram 6, E E', and diagram 8, Y), in a manner which 
wonderfully accords with the direction of the fibres composing one or other of the mus- 
culi papillares (Plate XVI. compare Y of diagram 9 withy of figs. 12 & 13, Plate XII.). 
Having constructed one half of the typical ventricle, it is necessary, to complete the 
other, to lay a second sheet upon the original one, at a slight angle, as represented 
in diagram 2, Plate XV. *, after which the sheets are rolled up (the one within the 
* In the diagram adverted to, it will be observed I have represented on the comers of the sheets two imagi- 
nary papillary muscles (X, Y), for the purpose of showing the positions they occupy in the interior of the cone 
when the sheets are rolled up. 
