Talk:Paper - The development and evolution of the "papillary" ridges and patterns on the volar surface of the hand

THE DEVELOPMENT AND EVOLUTION OF THE “ PAPILLARY ” RIDGES AND PATTERNS ON THE VOLAR SURFACE OF THE HAND! By EveLyn Joun Evatt, Assistant in Anatomy, University College, Cardiff.

THE following account is based on observations made almost exclusively on the human hand. The dates given are rough approximations; they were inferred by comparing the foetuses from which the specimens were taken with the figures found in the section on “General Embryology” in the Text-Book of Anatomy, edited by Cunningham. The volar surface of the developing human hand presents a number of well-detined pads; they are first recognisable about the sixth week of intrauterine life, and have attained their maximum relative development by the fifteenth week ; after this period they are to be regarded as decrescent. The morphology of these pads has been worked out by Johnson, Klaatsch, Inez L. Whipple, and Wilder with a thoroughness that would seem to leave nothing to be desired. In the adult the sites of the pads are occupied by papillary (epidermic, Inez L. Whipple) ridge patterns. The design formed by these ridges on the volar surface of a terminal phalanx may be regarded as the most typical expression of a pattern, and the term “pattern” in the text will be used to describe such formations. For a full and detailed description of the outlines and cores of finger-tip patterns, Galton’s Finger Prints may be consulted.

The method employed in the preparation of the specimens, from a study of which the results stated in this paper were arrived at, was briefly as follows: the skin was removed from the volar surface of the terminal phalanx of the thumb, stained, dehydrated, and cleared in clove oil; camera-lucida drawings were made of the surface views of the pieces under the microscope, the pieces were then embedded in paraftin, and a number of vertical sections were taken from each; these were mounted and photographed.

An undifterentiated area of nucleated cells is all that can be seen in a surface view of the skin at seven and a half weeks: a vertical section from this piece (fig. 1) shows that the deepest layer of the

1 Read at the Anatomical Society of Great Britain and Ireland, March 1906. “ Papillary ” Ridges and Patterns on the Volar Surface of the Hand 67

epidermis consists of columnar cells. The epidermis lies flat upon the corium, from which it is demarcated by what appears to be a welldefined basement membrane. The epidermis in a number of these sections was widely separated from the corium, indicating that these two surfaces were but loosely attached to each other. The surface is quite smooth.

Surface views of layers of skin, at eleven weeks, present a striped appearance, dark and light lines alternating, and designs technically known

Fic. 1.—Vertical’ section of skin, foetus aged seven and a half weeks e, epidermis ; ¢, coriuin ; ¢.., layer of columnar cells ; b.m., ‘‘ basement membrane.” - cite mere NG ,

as patterns are to be seen. Fig. 2 is a vertical section from one such piece. It shows the epidermis as having invaded the underlying corium in a wavy outline; the layer of columnar cells is well marked and follows the undulations of the epidermis; the remaining cells of the epidermis are polyhedral in shape and all ‘traces of a basement membrane have disappeared ; the surface is quite smooth, there are no “epidermic” ridges. It may be as well to state here that the term “subdermal” ridges in the text will be held to apply to the wedge-shaped epidermal invasions (fig. 2). Inez L. Whipple has happily suggested the term “epidermic” ridges for the minute ribs which cover the volar surface of the hand, and of which an impress may be taken. 68 Mr Evelyn John Evatt

Although, from about the tenth week onwards, surface views of cleared pieces of skin from the volar surface of the terminal phalanges of the tinger-tip pads present distinct typical patterns, and later the positions of the rudimentary sweat glands, it is not until about the eighteenth week that the cells on the bases or free surfaces of the subdermal ridges are found to have proliferated and to lie in ribs upon the surface (figs. 2 and 3); the ribs are the rudiments of the epidermic ridges. Sections at this age (fig. 3) show the summits of the papille of the corium lying at the bottom of the

Fic. 2.—Vertical section of skin, fuwtus, aged eleven weeks, shows four ““subdermal” ridges. ¢, epidermis: c, corium; c.d., layer of columnar cells ; b, base of a subdermal ridge.

troughs formed between collateral epidermic ridges, while from the apices of the subdermal ridges sweat glands are seen to be passing into the corium. Traces of the sweat glands are found long before the epidermic ridges have appeared. An examination of the skin from the finger-tips of numerous foetal hands in which the subdermal ridges had appeared, revealed the presence of a variety of patterns, such as one might expect to find on the finger-tips of an adult hand, although the patterns were not present on the surface.

A study of the accompanying figures and of the text will have shown that the following facts are demonstrable.

Patterns are found only on the sites originally occupied by the pads, “ Papillary” Ridges and Patterns on the Volar Surface of the Hand 69

elsewhere on the palm the ridges are disposed transversely or obliquely to

the long axis of the limb.

Patterns are present below the surface before their counterparts (epidermic ridge patterns) appear on the surface of the skin.

In ontogeny the patterns are primordial, that is to say, the relative positions of the ridges forming a pattern are primitive conditions.

The following statement of a theory of the evolution of the epidermic ridge patterns in phylogeny is suggested.

Fic, 3.— Vertical section of skin, foetus aged eighteen wecks. ¢, epidermis ; c, corium ; s.g., sweat glands ; p, papillary or epidermic ridges.

The epidermis originally invaded the corium in parallel ridges. This corrugating invasion tended, no doubt, to strengthen the attachment between the two structures.

The ridges were at first disposed transversely to the long axis of the limb, both over the pads and the rest of the palm, a disposition which may be observed on the adult hand at the bases of the patterns. Hepburn and Klaatsch have drawn attention to this transverse disposition of the ridges on the ventral surface of the prehensile tail of the nigger monkey; the transverse arrangement is particularly well marked on the terminal

segment. When the hand assumed the function of grasping in the early history 70 Mr Evelyn John Evatt

of man, the pads tended to follow the stresses of prehension; therefore the finger-tip pads, with their associated subdermal ridges, assumed a distal inclination, and the ridges were thrown into arches with their convexities directed distally. The remaining pads, with their respective ridges in obedience to the stresses of prehension, inclined proximally, and these particular ridges formed arches whose convexities were directed towards the base of the hand.

At first the inclining of the pads by the stresses of prehension would throw the ridges into a series of plain arches, it therefore appears that the “plain arch” is the most rudimentary of the patterns; later the more complex patterns were evolved as a result of the inclining of the pads with their associated subdermal ridges in the varying directions of the stresses of prehension.

A “plain arch” pattern may be experimentally produced by laying lengths of cord in parallel rows across a cone of some plastic material, eg. modelling clay, and then shoving or dragging over the summit of the cone. The pieces of cord representing ridges will now be seen to be drawn into arches, the degree of arching being proportional to the amount of the stress of prehension, and the plain-arch pattern is produced.

The different phases in the transition of a transverse ridge to an arch, loop, or whorl may be traced on their respective finger-tip patterns. In any one of these patterns, the ridges at the proximal end of the pattern, where the inclining of the pad was least, are disposed transversely, whereas at the centre, where the inclining was greatest, the ridges are thrown into forms characteristic of core centres ; and finally, from the centre to the distal end, where the inclining was intermediate in amount, the ridges are seen to be in arches successively more open. The subdermal ridges (fig. 2) did not yield under pressure to the same extent as the intervening shallower portions of the epidermis, they were consequently more exposed to pressure, and as this caused them to hypertrophy, they came to be elevated in ribs above the level of the surface (fig. 3); these ribs constituted epidermic ridges, and as they were moulded on the subdermal ridges, they produced a faithful replica of them and delineated the underlying pattern. “ Papillary ” Ridges and Patterns on the Volar Surface of the Hand 71

BIBLIOGRAPHY.

Gatton, Finger Prints, 1892.

Hepsurn, Anat. Anz. Bd. xiii., No. 16, and The Scientific Transactions of the Royal Dublin Society, vol. i. (series 2).

Jonnson, “Pads on the Palm and Sole of the Human Fetus,” Am. Nat., vol. xxxiii.

Kuaatscu, “Morphologie der Tastballen der Siugethiere,” Jahrbuch, xiv., Leipzig, 1888.

Inzz LL. Wuiprite, “The Ventral Surface of the Mammalian Chiridium,” Zeitschrift siir Morphologie und Anthropologie, Bd. vii. (S. 261-368).

Wiper, ‘‘ Palms and Soles,” American Journal of Anatomy, vol. i., No. 4.