IN THE VENTRICLES OF THE VERTEBRATE HEART. 
465 
appears to me that in order to produce the right ventricle, and explain the relation 
existing between the right and left ventricles anteriorly, posteriorly, and septally, all 
that is necessary is to push in the anterior wall (Plate XVI. diag. 15, a) in an antero- 
posterior direction until it touches the posterior one (B), in imitation of the constructive 
process. As however, in pushing in the anterior wall until it touches the posterior one 
a double septum is produced which is unattached posteriorly, it is necessary, to complete 
the structure, to suppose the fibres forming the posterior border of the septal duplica- 
ture as coalescing with corresponding fibres of the posterior wall, until the central layer is 
reached (Plate XVI. diag. 17, K) ; whilst the fibres of the two halves of the duplicature 
itself pass through and are blended with each other to the same extent (E J). If the 
constructive process be so imitated, it will be seen that not only are two ventricles (C, D) 
produced, each of which has fibres peculiar to itself (I H, F E), but, what is remark- 
able, that these ventricles are united to each other posteriorly (K) and septally (E J) by 
a series of fibres, which are common to both, i. e. fibres which belong partly to the one 
ventricle and partly to the other, precisely as in the ventricles themselves. The fibres 
moreover of the left or principal ventricle form four systems of conical spirals, two 
external and two internal — the former winding from above downwards from left to 
right, to twist rapidly round in a whorl at the apex, where they are continuous with the 
two internal systems *, winding in an opposite direction, from below upwards and from 
right to left. 
The fibres of the right ventricle, on the other hand, form only segments of spirals — 
they being continuous with each other not at one point as in the left ventricle, but 
throughout the track for the anterior coronary artery (A). That the foregoing arrange- 
ment approaches very closely to, if it is not identical with, that occurring in the 
ventricles of the adult heart, may be ascertained in various ways. 
1st. When the right and left ventricles (Plate XIII. figs. 18, 21, & 24) are dissected 
from without inwards, the layers constituting the right ventricular wall (ff") gradually 
increase in thickness, and pass through the several changes in direction met with in the 
layers of the left ventricular wall ( d d'), clearly showing that the right and left ventricles 
are constructed on the same type. As, however, the left ventricle, as will be shown 
presently, is the more complete of the two, it is more natural to suppose that the right 
ventricle is a segment of the left one, than the reverse. 
2ndly. When both ventricles are dissected at the same time, the fibres forming the 
external layers posteriorly (Plate XIII. fig. 21) are for the most part common alike to 
the one ventricle and the other f; in other words, the fibres on the back part of the left 
ventricle (/) cross over the posterior coronary track (j), and pass on to the right 
* The external and internal systems, as has been explained, are rendered continuous at the base by bending 
over until they meet each other. Similar remarks apply to the fibres at the base of the right ventricle. 
f The fibres forming the left apex are peculiar to itself, and belong exclusively to the left ventricle. This 
distribution of the fibres is accounted for by the fold which I believe forms the right ventricle beginning fully 
half an inch above the apex in question. 
