IN THE VENTRICLES OE THE VERTEBRATE HEART. 
453 
to regard the left ventricle as the typical or complete one, the right ventricle being a 
mere segment or portion nipped off at some period or other from the left. 
IX. If the right ventricular walls be cut through immediately to the right of the 
track for the anterior and posterior coronary arteries, so as to detach the right ventricle 
without disturbing the septum, and the septum be regarded as forming part of the left 
ventricular wall, it will be found that the fibres from the right side of the septum, at no 
great depth from the surface, together with the external fibres from the left ventricular 
wall generally, enter the left apex in two sets ; and if their course in the interior be traced, 
they are observed to issue from the left auriculo-ventricular opening, also in two sets ; in 
other words, the left ventricle is bilateral. I would particularly direct the attention of 
investigators to this bilateral distribution of the fibres, as it has been hitherto overlooked, 
and furnishes the clue to the arrangement of the fibres of the left ventricle. 
X. The double entrance of the fibres at the left apex, and their exit in two portions 
from the auriculo-ventricular opening at the base, are regulated with almost mathema- 
tical precision ; so that while the one set of fibres invariably enters the apex posteriorly, 
and issues from the auriculo-ventricular opening anteriorly, the other set as invariably 
enters the apex anteriorly, and escapes from the auriculo-ventricular opening posteriorly. 
But for this disposition of the fibres, the apex and the base would have been like the 
barrel of a pen cut slantingly or lopsided, instead of bilaterally symmetrical as they are. 
XI. The two sets of fibres which constitute the superficial or first external layer of 
the left ventricle, and which enter the left apex in two separate portions or bundles, are 
for the most part continuous in the interior with the musculi papillares, to the free 
ends of which the chordae tendineae are attached. These columns occupy different 
portions of the left ventricular cavity, and give a very good idea of the symmetry which 
prevails throughout the left ventricular walls. 
Lastly. The apex is opened into and enlarged, and the auriculo-ventricular orifice 
widened, by the removal of consecutive external and internal layers, from the fact of 
the left ventricular cavity tapering in two directions and forming a double cone. 
There are other points worthy of mention, such as the construction of the septum, 
fleshy pons, and conus arteriosus, the varying thickness of the right and left ventricular 
walls, the shape of the right and left ventricular cavities, &c. To these, however, 
allusion will be more conveniently made subsequently. 
As the structure of the ventricles, with one or two exceptions, is the same in all 
mammals, man included , I have chosen to describe the arrangement of the fibres in the 
ventricles of the sheep and calf, from the readiness with which the hearts of these animals 
may be obtained. My descriptions, however, will by no means he confined to them. 
Points to be attended to in the dissection of the left or typical ventricle. The points 
to be kept more particularly in view when dissecting the left ventricle are these 
1st. The different angles made by the fibres of the several layers, with an imaginary 
vertical line drawn from base to apex, as they issue from the auriculo-ventricular open- 
ing and enter the apex. 
mdccclxiv. 3 p 
