488 
DR. PETTIGREW ON THE ARRANGEMENT OF THE FIBRES 
smaller and smaller curves as they approach the apex, where they involute or turn in ; 
whereas the two sets of internal ones, which" wind from the apex of the cone to the base 
in a direction from right to left upwards, make larger and larger curves as they approach 
the base, where they evolute or turn out. The external and internal fibres have therefore 
different directions in different parts of their respective courses ; and as the spirals formed 
by the external and internal sets cross and overlap at every half turn of their progress, 
we are in this way furnished not only with fibres having different degrees of obliquity, 
but also with different layers or strata of fibres. 
Since the artificial ventricle, constructed as described, presents all the peculiarities of 
the typical or left ventricle, it is obvious that if, beginning a little above its apex, a por- 
tion of the anterior wall is pushed in (Plate XVI. diagram 15, A ; Plate XV. compare 
with m of fig. 50, and with o l, pn of fig. 45) until it touches the posterior one (Plate 
XVI. diagram 15, B ; Plate XV. compare with g of fig. 50), and allowance made for the 
passing through and blending of the lines posteriorly (Plate XVI. diagram 16, G) and 
septally (Plate XVI. diagrams 16, HK; also diagrams 17 &18, H E), as recommended 
at page 464, and indicated by the division of the primary tube in the embryo, two ven- 
tricles (C & D) would be produced, resembling the true ventricles (compare with b l of 
figs. 49, 50, & 51, and op of fig. 45, Plate XV. more particularly; also with o of fig. 23, 
Plate XIII.) as closely as the artificial single ventricle resembles the left or typical 
ventricle. This is so evident that further explanation is unnecessary. 
With these remarks I finish the description of an avowedly difficult structure ; and, in 
taking leave of the subject, I trust I may not be charged with forcing analogies and 
instituting resemblances where none exist. Having no theory to serve, my sole aim 
throughout the investigation has been the elucidation of truth ; but where that is so 
cunningly, and, it may be added, so successfully concealed, it has often been exceedingly 
difficult to arrange the materials with which my numerous dissections supplied me, so 
as to preserve a sequence in the description while I at the same time contrasted the 
direction of the fibres composing the several layers with each other. The method 
employed in demonstrating the ventricles in the present instance, viz. by consecutive 
layers, while it is by far the most natural yet proposed, is, I believe, the best calculated 
to afford intelligible results ; for as layers or strata of fibres unquestionably exist, and 
these intersect each other at various angles, and are found at different depths from the 
surface, it follows that all attempts to display in any individual heart, what can only be 
shown in a series of hearts, must prove abortive. The great advantage of conducting 
the dissection from without inwards by the removal of consecutive layers consists in its 
preserving the relation of the several layers to each other, and in showing how the fibres 
of each are continuous at the base and at the apex. This is well seen in the first seven 
figures of Plate XII., where the layers of the left ventricle are exposed posteriorly ; for 
by placing fig. 7 within 6, figs. 7 & 6 within 5, and so on until all the figures are placed 
within fig. 1, not only are the relations of the several layers to each other maintained, 
but the ventricle is as it were rendered transparent, so that one may trace in imagina- 
