Initiative in Evolution :: CHAPTER XIX. FLEXURES OF THE PALM AND SOLE.

CHAPTER XIX. 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

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

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.

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 D2, 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.

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.

Fig. 72.—Foot of common squirrel.

Fig. 73.—Flexures on foot of vulpine phalanger.

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.—Foot of loris.

Fig. 75.—Foot of ring-tailed lemur.

Fig. 74, the highly-developed prehensile foot of the loris.

Fig. 75, the foot of a ring-tailed lemur.

Fig. 76.—Foot of squirrel-monkey.

Fig. 77.—Foot of macaque.

Fig. 76, the foot of a squirrel-monkey (Chrysothrix Sciurea).

Fig. 77, the foot of a macacus (Macacus cynomologus).

Fig. 78.—Foot of gibbon.

Fig. 79.—Hand of chimpanzee.

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.

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.

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