IN THE VENTEICLES OF THE VEETEBEATE HEAET. 
485 
the most perfect manner with the structure exhibited in the left ventricle (Plate XII. 
compare the fibres marked ff of fig. 1 with those marked o o' o" of fig. 8). Nor 
does the coincidence stop here. If the cone composed of the spiral lines constructed 
as above (Plate XVI. diagram 4) be examined in a direction from without inwards, it 
will be seen that its walls on the one aspect consist of four distinct layers — two external 
(A A', B, compare with the direction of the fibres in Plate XII. figs. 1 & 3) and two 
internal (D, E E', compare with the direction of the fibres in Plate XII. figs. 5 & 8) ; 
and on the other (Plate XVI. diagram 5) of three — one external (B B', compare with 
the direction of the fibres in Plate XII. fig. 2), one internal (D D', compare with the 
direction of the fibres in Plate XII. fig. 6), and one central (C C' C", compare with the 
direction of the fibres in Plate XII. fig. 4) ; and, what is remarkable, that the lines 
entering into the formation of the external layers run in different directions, and cross 
those forming the internal layers as in the ventricle itself (Plate XII., compare the 
direction of the external fibres in figs. 1, 2, & 3 with that of the internal fibres in figs. 5, 
6, & 7). Another point of resemblance, deserving of particular attention, is the regional 
distribution of the layers themselves, that side of the cone which is composed of four 
layers (Plate XYI. diagram 4) showing how one layer enters into the formation of the 
extreme apex (C), two into the extreme base (A E') and the portion of the ventricular 
wall immediately above the apex (B D), three into the portion of the wall immediately 
below the base, and four into the upper and more central portion (B' D'), — the other or 
remaining side which is composed of three layers (Plate XYI. diagram 5), showing 
that one layer enters into the extreme apex (C), two into the extreme base (R), and 
three into the upper and central portion (C C"). This arrangement proves, curiously 
enough, that the model ventricular wall, like the true one, tapers in two directions, viz. 
towards the base (Plate XII. compare with s of figs. 13, 14, & 15) and towards the apex 
(Plate XII. compare with s/ of figs. 13, 14, & 15). There are other points of resem- 
blance. If the marginal line* (Plate XVI. diagram 3, ABODE) of the sheet rolled 
up as described (and which may be taken to represent the first and seventh layers of the 
left ventricle) be traced, it will be found to proceed in a spiral nearly vertical direction, 
and to run from the extreme base (A) to the extreme apex (C), at which point it reverses 
its course and enters the interior, after which it returns to the extreme base, making one 
turn and a half of a spiral in either direction, as in Plate XII. figs. 1 & 8. It in this 
manner embraces in its convolutions all the other lines, the initial letters of which are 
H M R Y, in the same way that the first layer and its internal continuation, the seventh 
layer, overlaps or embraces all the deeper layers (Plate XII. vide figs. 2, 3, 4, 5, and 6), 
all of which are included within and embraced by figs. 1 and 7). If, on the other hand, 
a second line a little removed from the marginal line (Plate XV. diagram 1, F G H I J), 
* I have chosen to speak of individual lines, as admitting of more precise description ; hut it would he equally 
correct to speak of the lines confined to any particular portion of the sheet, for it is the aggregate of the lines 
in certain portions of it which constitutes the layers. Thus the lines composing one-third of the sheet go to 
form the first external layer and the last internal (Plate XYI. diagram 4, A A' & E E'). 
MDCCCLXIV. 3 T 
