IN THE VENTRICLES OE THE VERTEBRATE HEART. 
499 
Diagram 10. Symmetrical cone produced by rolling two sheets of net within each other. 
Shows how the symmetry of the cone is maintained by the sheets winding 
from opposite points, the one, the anterior (A B), winding from before back- 
wards, or from right to left, to enter the apex posteriorly (F), the other, the 
posterior (C D), winding from behind forwards, or from left to right, to enter 
the apex anteriorly (E) (Plate XVI. fig. 55, compare with ef\ Plate XII. 
fig. 11, compare with Jcl). See pages 486 & 487. 
Diagram 11. Interior of symmetrical cone, as seen at diagram 7, formed by the rolling 
of two sheets of net within each other. Shows how the position and shape 
of the spiral nearly vertical anterior (Y) and posterior (X) musculi papillares 
may be imitated (Plate XII. figs. 12 & 13, compare with y x). See pages 
486 & 487. 
Diagram 12. Two sheets of paper with parallel lines drawn upon them, rolled within 
each other, and then permitted to spring open (seen from above). Imitates 
the double entrance of the fibres at the left apex. Compare the direction of 
the lines on the sheet ABE with the direction (Plate XVI. fig. 55) of the 
fibres a b e, and also the direction of the lines in the sheet CDF with the 
direction of the fibres c df of the same figure. 
Diagram 13 represents the course pursued by a single fibre, how it winds from the 
base to the apex in one direction, and from the apex to the base in another, 
so as to return to the point from which it set out. It also shows how the 
fibre is continuous towards the apex and the base. See page 485. 
ABC. External portion of the fibre winding from above downward, or from 
the base to the apex. 
D. Point at which the fibre enters the apex and alters its direction. 
E F. Internal portion of the fibre winding from below upward, or from the 
apex to the base, to return to the point A. 
Diagram 14 represents the course pursued by two fibres, each of which is similar to 
that figured at diagram 13. In this diagram the external portion of one of 
the fibres (ABC) winds from behind forwards and enters the apex ante- 
riorly (D), the external portion of the other fibre (GHIJ) winding from 
before backwards and entering the apex posteriorly (K). The external por- 
tions of the fibres are therefore symmetrically disposed with reference to each 
other. Similar remarks apply to the internal continuations of these fibres 
(E G H, LA M), which are only partially seen. The external and internal 
portions of the fibres are continuous, and when seen from above appear to 
form complete circles. See pages 486 & 487. 
Fig. 55. Sheep’s heart separated into its bilateral elements. See pages 457, 486, & 487. 
a b. Anterior fibres entering the left apex posteriorly (e). 
c d. Posterior fibres entering the left apex anteriorly (f). 
Diagram 15 shows how by pushing in the anterior wall (A) of the typical or left 
