FLEXURES OF THE PALM AND SOLE.
Those flexures of the palmar and plantar skin which are called by
Galton chiromantic creases, and said by him to be no more significant
to others than palmists than the creases of old clothes, have received
a remarkable amount of pseudo-scientific attention since earliest
times in Chinese and Greek history. The former even added podoscopy to
their chiromancy. The line of life, the line of the head, the line of
the heart, the line of fortune and that of the liver, figure freely
in fortune-telling of modern drawing-rooms by women who ought to be
in Holloway gaol, but are not. The gipsies, their predecessors and
equally honest teachers, did not employ such high-sounding words, but I
believe that by observing closely the bearing, looks, dress and manner
of their dupes, while pretending to study their palms, both classes of
practitioners, like phrenologists, are able to tell a good deal of what
their customers _are_, and being shrewd persons they are able to guess
pretty well what they _will be and will do_.
I agree with Galton that these creases of hand and foot are no more
significant than those of an old coat-sleeve, a pair of trousers, or
boots; but they are not less significant of certain muscular habits of
the wearers of those articles.[65]
[65] Galton might have referred by way of illustration to an immortal
woman in _Martin Chuzzlewit_, who shall be nameless here.
The flexures in question are in line with the subjects of the two
preceding chapters, and require little more description in detail than
is afforded by the accompanying illustration of mammalian hands and
feet.
Description of Flexures.
There are two classes which may be conveniently called here Primary and
Secondary, the latter being too variable and accidental for further
notice. The former lie in three main directions and are longitudinal,
oblique or transverse. They represent in graphic characters the nature
and degree of the functions exercised by muscles moving the joints
which underlie them, and are often called “flexion-lines.” They are
“folds so disposed that the thick skin shall be capable of bending in
grasping while it at the same time requires to be tightly bound down
to the skeleton of the hands and feet, so as to prevent slipping of
the skin which would necessarily lead to insecurity of prehension,
just as the quilting and buttoning down of the covers of furniture
by upholsterers keeps them from slipping. For this purpose the skin
is tied by fibres of white fibrillar tissue to the deep layer of the
dermis along the lateral and lower edges of the palmar fascia and to
the sheaths of the flexor tendons. The folds, therefore, which are
disposed for the purpose of making the grasp secure, vary with the
relative lengths of the metacarpal bones, with the mutual relations
of the sheaths of the tendons and the edge of the palmar and plantar
fascia.... The sulci are emphasised because the subcutaneous fat,
which is copious in order to pad the skin for the purpose of holding,
being restricted to the interval between the lines along which the
skin is tied down, makes these intervals project, and these are the
monteculi.”[66]
[66] A. Macalister, _Palmistry Encycl. Brit._, 11th Edition.
This account of them from a leading anatomist shows that not for
nothing have these creases been evolved. They are inherited, have an
important function and are worthy of study in their humble way: they
may be even dignified with the name “character.”
They are often double over the joints of the fingers and toes, but,
from the functional point of view and for simplicity, may be reckoned
as single.
Chief Types.
[Illustration: Fig. 71.--Flexures on palm of right hand. Drawing made
from impression.]
The most common types of them in the hand of man are shown in the
example given in Fig. 71.
1. A flexure over each phalangeal joint.
2. A flexure at the bases of the digits.
3. A flexure over the metacarpo-phalangeal joints of D 2, 3, 4 and 5
with an oblique direction, called _linea mensalis_.
4. A flexure over these same joints and oblique in direction, but
nearer to the wrist--the _linea cephalica_. These flexures 3 and 4,
though arising from the flexion of one set of joints should be looked
at as separate folds because of their time-honoured popular names.
5. A curving flexure surrounding the thenar eminence, extending from
the centre of the wrist along the palm and terminating at the radial
border.
6. Variable longitudinal and oblique flexures not specified, which I
have called secondary.
[Illustration: Fig. 72.--Foot of common squirrel.]
[Illustration: Fig. 73.--Flexures on foot of vulpine phalanger.]
[Illustration: Fig. 74.--Foot of loris.]
[Illustration: Fig. 75.--Foot of ring-tailed lemur.]
Meaning.
Whatever be the meaning and origin of these flexures they are not mere
folds such as one makes in a garment and leaves it so. Action, function
and fitting of the structures of the hand and foot are involved in
their history. They may loosely be termed “ergographs” without any
reference to the exact measurement of work done. No proper idea can
be formed of them if the original function and evolution of the
walking-pads of earlier mammals be omitted. If one goes back and back
until one reaches some lowly marsupial as a _vulpine phalanger_, or
insectivore such as a common _hedgehog_, one may even metaphorically
see these animals being fitted by a shoemaker with rude shoes or
walking-pads for the better locomotion on or under ground, or in the
branches of trees. These pads are projecting masses of hard fat with
fibrous tissue interspersed and they early become fitted or adapted
_to_ or _by_ the use to which they are put. It is impossible to suppose
that certain rudimentary pads are devised by selective processes prior
to the altered habits of walking of the animal that acquires them. From
the shoemaking point of view the fashion is rough and generalised, and
the changing habits of the animal adapt the shoe by degrees to the
function employed, much as many a private soldier knows to his cost
that he has had to adapt slowly and painfully his army boot to his
particular foot. This process in an early pedestrian mammal involves
the breaking up and limiting of the rudimentary pads by sulci in the
dense skin, and the process of struggle and adjustment between the
pads and their bordering furrows issues in the characteristic flexure
of each mammal. From experiences in the human body one knows how
easily fibrous adhesions between the skin and deeper parts, notably in
cases of Dupuytren’s contraction of the palmar fascia, are formed by
close apposition of the two layers. Such adhesion is precluded when
much movement of the part occurs, but _ex-hypothesi_ the rudimentary
flexures are distinguished by absence of movement, and the conditions
for fixing down the deeper layers of the skin to the bones beneath are
clearly present. That these are not indifferent structures is evident
from what Macalister says, and though they be small or even trivial may
be held to have acquired at some time or other selective value. Their
early stages would necessarily be too tentative, varied and slight to
acquire such value.
[Illustration: Fig. 76.--Foot of squirrel-monkey.]
[Illustration: Fig. 77.--Foot of macaque.]
[Illustration: Fig. 78.--Foot of gibbon.]
[Illustration: Fig. 79.--Hand of chimpanzee.]
Fig. 72 is a sketch of the hand and foot of a squirrel (Sciurus) and
the numbers 1, 2, 3, 4, 5 and 6 are placed conspicuously on the walking
pads in accordance with the teaching of Dr. and Mrs. Wilder Harris as
to the six palmar and plantar walking-pads, of which the typical palm
and sole is constructed. The thick, black lines indicate the flexures
formed round the pads by the exercise of the functions of the hand and
foot.
Fig. 73 represents the clumsy, thick walking-pads of a marsupial the
vulpine phalanger, _trichosurus vulpecula_.
Fig. 74, the highly-developed prehensile foot of the loris.
Fig. 75, the foot of a ring-tailed lemur.
Fig. 76, the foot of a squirrel-monkey (Chrysothrix Sciurea).
Fig. 77, the foot of a macacus (Macacus cynomologus).
Fig. 78, the foot of a gibbon.
Fig. 79, the hand of a chimpanzee and here the resemblance to the
_hand_ of man and _not to the foot of man_ is very striking.
A description has already been given of man’s flexures of the palm.
[Illustration: Fig. 80.--Drawing of flexures of sole of foot in young
adult.]
Fig. 80 is a careful drawing of the sole of a young active woman
with a well-formed foot, and there is little typical in the mode of
arrangement of its creases except the slight tendency to transverse
lines of flexure. In all the feet I have examined I have found no
single flexure that is constant, and the longitudinal ones here shown
are often absent.
Reviewing these examples one observes an evolutional decay of a minor
but necessary piece of mechanism of the Primate hand and foot. The
general similarity, _mutatis mutandis_, of the flexures of the palm
and sole in Primates is very noticeable, and is associated with the
strong prehensile power of the foot of all the forms below man. In
the cases of the two apes shown in this series, the resemblance is
still well marked, more so even in the chimpanzee than the gibbon, so
that the disappearance from the sole of man’s foot of any important
flexure is very significant of his loss of prehensile and gain of
locomotive perfection, and I find it impossible to conceive any process
of evolutionary change where a loss of the flexures of a prehensile
foot could come under the power of selection, on its own merits. On
the other hand this remarkable instance of disuse of a formerly useful
structure is adequately accounted for by the evolution of an organ
like the human foot which in course of long periods of time became an
organ of one function. Weismann might score a point over Spencer from
his laboured explanations of man’s dwindling little toe, but here,
I submit, he would have had to take refuge in silence, and pass to
characters of a higher and more debateable kind.