6. Spiral.—When the transverse flexures described in 1 do not pass gradually from straight lines into curves, but assume that form suddenly with a more rapid divergence, a semicircular space is necessarily created, which stands upon the straight and horizontal lines below, as it were upon a base. This space is filled by a spiral either of a simple or composite form. The term ‘simple’ spiral is to be understood in the usual geometric sense. I call the spiral ‘composite’ when it is made up of several lines proceeding from the same centre, or of lines branching at intervals and twisted upon themselves. At either side, where the spiral is contiguous to the place at which the straight and curved lines begin to diverge, in order to enclose it, two triangles are formed, just like the single one that is formed at the side of the oblique sinus.
7. Ellipse, or Elliptical Whorl.—The semicircular space described in 6 is here filled with concentric ellipses enclosing a short single line in their middle.
8. Circle, or Circular Whorl.—Here a single point takes the place of the short line mentioned in 7. It is surrounded by a number of concentric circles reaching to the ridges that bound the semicircular space.
9. Double Whorl.—One portion of the transverse lines runs forward with a bend and recurves upon itself with a half turn, and is embraced by another portion which proceeds from the other side in the same way. This produces a doubly twisted figure which is rarely met with except on the thumb, fore, and ring fingers. The ends of the curved portions may be variously inclined; they may be nearly perpendicular, of various degrees of obliquity, or nearly horizontal.
In all of the forms 6, 7, 8, and 9, triangles may be seen at the points where the divergence begins between the transverse and the arched lines, and at both sides. On the remaining phalanges, the transverse lines proceed diagonally, and are straight or only slightly curved.”
(He then proceeds to speak of the palm of the hand in men and in monkeys.)
CHAPTER VI
PERSISTENCE