484 
DE. PETTIGEEW ON THE AEEAN GEMENT OE THE EIBEES 
The comparative size of the right and left ventricular cavities has been the subject of 
considerable discussion, and is not likely soon to be set at rest, from the yielding nature 
of the ventricular parietes. 
Inference deduced from a consideration of the Arrangement of the Fibres 
in the Ventricles of the Bird and Mammal. 
Without presuming dogmatically to assert that the ultimate arrangement of the fibres 
of the ventricles of the bird and mammal is reducible to any known mathematical law, I 
cannot omit mentioning the fact that the arrangement in question can be so thoroughly 
imitated, even in its details, by certain mechanical contrivances about to be explained, 
that I would consider the present communication incomplete, were I not shortly to 
direct attention to them. 
If a sheet of paper, parchment, or any flexible material * whose length is twice that 
of its breadth, be taken, and parallel lines drawn on either side of it in the direction of 
the length, to represent the course of the fibres (Plate XV. diag. 1), all that requires to 
be done, in order to convert it into a literal transcript of one-half of the left or typical 
ventricle, is to lay it out lengthwise across a table, and, catching it by the right-hand 
distant corner, to roll or turn in towards one’s self a conical-shaped portion (C), and con- 
tinue the rolling process in the direction of the opposite or oblique corner (U), until 
three and a half turns of the sheet have been made and a hollow cone produced, as 
shown at diagrams 4 & 5, Plate XVI. If the sheet be so manipulated, it will be found 
that every line in it is converted into a double conical spiral, — the one-half of the spiral 
being external to the other half, and running from base to apex and from left to right 
(Plate XVI. diag. 3, A B), precisely as in the left ventricle (Plate XII. compare with the 
direction of the fibres in figs. 1 & 9) ; the remaining half, which is internal, running from 
apex to base, and from right to left (Plate XVI. diag. 3, D E ; Plate XII. compare with 
the direction of the fibres in figs. 7 & 8). Tracing the external spirals to the apex, they 
are seen to turn abruptly upon themselves at this point (Plate XVI. diagrams 3 & 4, C, 
diagrams 8 & 13, D ; Plate XII. compare with apex of fig. 10), to reverse their direction 
and enter the interior, where they are continuous with the internal spirals (Plate XVI. 
diagrams 4 & 6, DEE'; Plate XII. compare with the fibres marked k of fig. 4); and 
if the corners of the sheet be folded out at the base, as has been done at Plate XVI. 
diagrams 3, 4, 5, & 6, and the internal spirals traced from the apex, or from below up- 
wards (Plate XVI. diag. 3, H I J), they will be seen again to reverse their direction to 
become continuous with the external spirals (F G H), — an arrangement coinciding in 
* Very beautiful transparent models of the left ventricle may be made, by employing sheets of net of a large 
pattern, with threads of wool drawn through the interstices at intervals of an inch or so. Sheets of this 
nature have been photographed to illustrate this part of the paper. Yery convenient opaque models may be 
constructed by employing portions of newspapers, the reading of which represents the parallel lines. The 
author strongly recommends the use of these models, as a few minutes with such aids will throw more light on 
the course and direction of the fibres than hours of abstract reasoning without them. 
