IN THE VENTRICLES OE THE VERTEBRATE HEART. 
491 
the apex. Shows the anterior and posterior sets of fibres forming the seventh 
or last internal layer, twisting out of the interior of the left apex, in an oppo- 
site direction to that by which the anterior and posterior sets of fibres forming 
the first layer (with which they are continuous) entered. See pages 460, 461, 
& 462. 
y. Anterior musculus papillaris, cut across. 
x. Posterior musculus papillaris, cut across. 
m. Right apex. Shows comparative absence of spiral twist in the fibres com- 
posing it. 
Fig. 13. Left ventricle of the heart of a deer, opened anteriorly. Shows the anterior 
and posterior musculi papillares in situ. See pages 460, 461, & 462. 
y. The anterior musculus papillaris, winding in a spiral nearly vertical direc- 
tion from the apex to within a short distance of the base, where it ter- 
minates in a more or less flattened uneven head, the irregular surface 
being occasioned by muscular prominences which give off chordae tendinese 
to be inserted into the segments of the bicuspid valve. 
x. The posterior musculus papillaris, twisting from behind the anterior one, 
and winding in a spiral nearly vertical direction from the apex to within 
a short distance of the base, where it terminates like the anterior, in a 
flattened uneven head. 
s. Vertical section of the left ventricle, showing how the ventricular wall 
tapers towards the apex and the base. 
r. Fibrous stay connecting the posterior musculus papillaris with the septal 
side of the left ventricular cavity. 
Fig. 14. Left ventricle of the heifer’s heart, opened laterally. Shows the musculi papil- 
lares and the bicuspid valve as usually displayed, the spiral twist peculiar to 
the musculi papillares being inadvertently destroyed. See pages 460 & 461. 
v. Anterior or outer segment of the bicuspid valve, with the chordae ten- 
dineae (t) which proceed from each musculus papillaris terminating in it. 
s s'. Vertical section of ventricular wall, tapering towards the apex and the 
base. 
w. Termination of the spiral groove which forms one of the two hollows found 
between the spiral musculi papillares. This groove, or rather the cast 
taken from it, is seen throughout its entire extent at z w b of fig. 17. 
r. Fibrous stays connecting the anterior and posterior musculi papillares with 
the septal side of the ventricular cavity. 
z. Reticulated arrangement of the fibres lining the interior of the ventricle 
and forming the carnese columnse. 
Fig. 15. Left ventricle of a human heart, opened laterally. Shows a tendency on the part 
of the fascicular bundles forming the musculi papillares to remain separate, 
also the highly developed nature of the carnese columnae. See page 461. 
a. Aorta. 
