IN THE VENTRICLES OF THE VERTEBRATE HEART. 
475 
form. Usually it resembles the mould of a ploughshare ; i. e. it is more or less trian- 
gular, and slightly bent or twisted upon itself to suit the curve of the aorta. That it per- 
forms no very important function, and is not necessary for the attachment of the fibres 
of the septum, is abundantly proved by its absence in a great number of instances. 
The os cordis , as it has been termed, is generally met with in the hearts of the horse, 
ox, sheep, and deer, and very rarely in man, the seal, pig, dog, hedgehog, hare, rabbit, 
and cat. 
Lastly, the shape of the right ventricle is peculiar. Viewed vertically, it forms two 
irregular cones, a larger and inferior cone, and a smaller and superior one (the conus 
arteriosus). They spring from a common base and have widely separated apices. The 
bases of the cones correspond with a line drawn from the posterior portion of the right 
auriculo-ventricular opening (Plate XIV. fig. 31, c) to a point in the track for the 
anterior coronary artery, midway between the apex ( d ) of the right ventricle and the 
root of the pulmonary artery (Jc). The apex of the larger or inferior cone (Plate XIV. 
fig. 31) corresponds with the apex of the right ventricle ( d ), and the apex of the smaller 
or superior one with the root of the pulmonary artery (Jc). Viewed transversely or by 
means of transverse sections, the right ventricle is found to be concavo-convex (Plate XV. 
figs. 49, 50, & 51, £),its concavity being turned towards the convexity of the left (h) ; in 
other words, the right ventricle is as it were flattened out and applied to or round the 
left one. Viewed from before backwards, or in an antero-posterior direction, the right 
ventricle is found to be twisted upon itself (Plate XII. fig. 16, and Plate XIV. figs. 34, 
35, 36, & 37), the two cones of which it is composed twisting in opposite directions — 
the larger or inferior cone (Plate XII. fig. 16, lh m, and Plate XIV. fig. 37, p' q q') 
in a direction from left to right downwards, the smaller or superior one (Plate XII. 
fig. 16, h Jc, and Plate XIV. fig. 37, p w Jc) in a direction from right to left upwards. 
Second external layer of tJie right and left ventricles (Mammal). When the superficial 
or first external layer, which in the mammal is comparatively thin, is removed, the 
second layer (Plate XIII. fig. 21), composed of fibres similarly arranged to those taken 
away, is exposed. The fibres of the second layer posteriorly proceed in a spiral direc- 
tion from left to right downwards, and are for the most part * common to both ventri- 
cles (ff") ; i. e. the fibres found on the left ventricle (f) cross the posterior coronary 
track (/), and are found also on the right ventricle (ff") ; while the fibres on the 
anterior aspect, which also proceed in a spiral direction from left to right downwards, 
with the exception of a broad band at the base, dip in at the anterior coronary track to 
appear on the right third of the septum, where they are continuous with fibres having a 
corresponding direction (Plate XIII. fig. 22, g). The fibres of the second layer differ from 
those of the first in being slightly fascicular, and in issuing from the auriculo-ventricular 
openings (Plate XIII. fig. 21, b l) and entering the left apex and anterior coronary 
groove more obliquely. They further differ in having a more oblique direction. The 
fibres of the second layer are arranged in two sets, the one of which proceeds from rather 
* A few of the fibres of the second layer proceed to the left apex only. 
