462 
DR. PETTIGREW ON THE ARRANGEMENT OF THE FIBRES 
These grooves are important physiologically; for I find that in them the blood is 
arranged in spiral columns during the diastole, and that towards the end of the diastole 
and the beginning of the systole, it is made to advance in spiral waves from beneath on 
the segments of the bicuspid valve, and communicates to these structures a distinctly 
spiral upward movement, the amount of upward motion being regulated by the chordae 
tendineae to prevent retroversion and regurgitation. As the systole advances and the 
musculi papillares contract with the other portions of the ventricular wall, the seg- 
ments of the valve are gradually drawn down by the chordae tendineae in an opposite 
direction to that by which they ascended and tightened upon the rapidly diminishing 
columns of blood, so that they form a spiral dependent cone, whose apex is directed 
towards the apex of the ventricle*. 
Cast of the interior of the left ventricle {Mammal). 
That the fibres of the seventh layer have a spiral direction and enclose a conical- 
shaped spiral cavity, may be readily ascertained by a reference to Plate XII. fig. 17, 
which is taken from a photograph of a wax cast of the interior of the left ventricle of 
the deer. On carefully examining the engraving in question, the cavity will be found 
to taper and twist towards the apex (z), and also, though to a less extent, towards the 
base ( b ). The diminution of the cavity towards the base is so slight that it might be 
overlooked, were it not that it renders the auriculo-ventricular orifice more easily closed 
than it would otherwise be. 
Transverse sections of the left ventricle {Mammal). 
The amount of spiral made by a cast of the left ventricular cavity, as ascertained by 
transverse sections, rather exceeds a turn and a half. This is proved by dividing the 
ventricle transversely into six unequal portions, by placing the sections in exactly the 
same positions, and by comparing the long axes of such portions of the cavity as are 
found in the sections with each other, and with the long axis of the cavity of the right 
ventricle. It is necessary to make the sections unequal, as the spiral formed by the 
cavity is much more rapid towards the apex than the base — the success of this demon- 
stration depending on making the section in such positions as will intersect the spiral 
at every half turn of its progress. I have given views of five of the sections alluded to ; 
and it will be observed that in the first two sections towards the base (Plate XV. 
figs. 49 & 50), the long axis of the cavity {b) of the left ventricle is at right angles to 
the long axis of the cavity of the right ventricle {l). In the third section (Plate XV. 
fig. 51), the long axis of the cavity {b) of the left ventricle is parallel with the long axis 
of the cavity of the right ventricle {l), showing that the left ventricular cavity has made 
half a spiral turn. In the fourth section (Plate XV. fig. 52), the long axis of the left 
* For a detailed account of the action of the mitral and tricuspid valves, see paper by the author “ On the 
Relations, Structure, and Function of the Yalves of the Vascular System in Vertebrata,” Transactions of the 
Royal Society of Edinburgh, vol. xxiii. p. 761. 
