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 OFTHE HAND! By EveLyn Joun Evatt, Assistant in Anatomy,University College, Cardiff.THE following account is based on observations made almost exclusively onthe human hand. The dates given are rough approximations; they wereinferred by comparing the foetuses from which the specimens were takenwith the figures found in the section on “General Embryology” in theText-Book of Anatomy, edited by Cunningham. The volar surface of thedeveloping human hand presents a number of well-detined pads; theyare first recognisable about the sixth week of intrauterine life, and haveattained their maximum relative development by the fifteenth week ;after this period they are to be regarded as decrescent. The morphologyof these pads has been worked out by Johnson, Klaatsch, Inez L. Whipple,and Wilder with a thoroughness that would seem to leave nothing tobe desired. In the adult the sites of the pads are occupied by papillary(epidermic, Inez L. Whipple) ridge patterns. The design formed by theseridges on the volar surface of a terminal phalanx may be regarded as themost typical expression of a pattern, and the term “pattern” in the textwill be used to describe such formations. For a full and detailed descriptionof the outlines and cores of finger-tip patterns, Galton’s Finger Prints maybe consulted.The method employed in the preparation of the specimens, from astudy of which the results stated in this paper were arrived at, wasbriefly as follows: the skin was removed from the volar surface of theterminal phalanx of the thumb, stained, dehydrated, and cleared in cloveoil; camera-lucida drawings were made of the surface views of the piecesunder the microscope, the pieces were then embedded in paraftin, and anumber of vertical sections were taken from each; these were mountedand photographed.An undifterentiated area of nucleated cells is all that can be seen ina surface view of the skin at seven and a half weeks: a verticalsection from this piece (fig. 1) shows that the deepest layer of the1 Read at the Anatomical Society of Great Britain and Ireland, March 1906.“ Papillary ” Ridges and Patterns on the Volar Surface of the Hand 67epidermis consists of columnar cells. The epidermis lies flat upon thecorium, from which it is demarcated by what appears to be a well-defined basement membrane. The epidermis in a number of thesesections was widely separated from the corium, indicating that thesetwo surfaces were but loosely attached to each other. The surface isquite smooth.Surface views of layers of skin, at eleven weeks, present a stripedappearance, dark and light lines alternating, and designs technically known Fic. 1.—Vertical’ section of skin, foetus aged seven and a half weekse, epidermis ; ¢, coriuin ; ¢.., layer of columnar cells ; b.m., ‘‘ base-ment membrane.” - cite mere NG ,as patterns are to be seen. Fig. 2 is a vertical section from one suchpiece. It shows the epidermis as having invaded the underlying coriumin a wavy outline; the layer of columnar cells is well marked and followsthe undulations of the epidermis; the remaining cells of the epidermis arepolyhedral in shape and all ‘traces of a basement membrane have dis-appeared ; the surface is quite smooth, there are no “epidermic” ridges.It may be as well to state here that the term “subdermal” ridges in thetext will be held to apply to the wedge-shaped epidermal invasions (fig. 2).Inez L. Whipple has happily suggested the term “epidermic” ridges forthe minute ribs which cover the volar surface of the hand, and of whichan impress may be taken.68 Mr Evelyn John EvattAlthough, from about the tenth week onwards, surface views of clearedpieces of skin from the volar surface of the terminal phalanges of thetinger-tip pads present distinct typical patterns, and later the positions of therudimentary sweat glands, it is not until about the eighteenth week thatthe cells on the bases or free surfaces of the subdermal ridges are found tohave proliferated and to lie in ribs upon the surface (figs. 2 and 3); theribs 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 ofcolumnar cells ; b, base of a subdermal ridge.troughs formed between collateral epidermic ridges, while from the apicesof the subdermal ridges sweat glands are seen to be passing into thecorium. Traces of the sweat glands are found long before the epidermicridges have appeared. An examination of the skin from the finger-tips ofnumerous foetal hands in which the subdermal ridges had appeared, revealedthe presence of a variety of patterns, such as one might expect to find onthe finger-tips of an adult hand, although the patterns were not present onthe surface.A study of the accompanying figures and of the text will have shownthat 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 69elsewhere on the palm the ridges are disposed transversely or obliquely tothe 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 relativepositions of the ridges forming a pattern are primitive conditions.The following statement of a theory of the evolution of the epidermicridge 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. Thiscorrugating invasion tended, no doubt, to strengthen the attachmentbetween the two structures.The ridges were at first disposed transversely to the long axis of thelimb, both over the pads and the rest of the palm, a disposition which maybe observed on the adult hand at the bases of the patterns. Hepburn andKlaatsch have drawn attention to this transverse disposition of the ridgeson the ventral surface of the prehensile tail of the nigger monkey; thetransverse arrangement is particularly well marked on the terminalsegment.When the hand assumed the function of grasping in the early history70 Mr Evelyn John Evattof man, the pads tended to follow the stresses of prehension; therefore thefinger-tip pads, with their associated subdermal ridges, assumed a distalinclination, and the ridges were thrown into arches with their convexitiesdirected distally. The remaining pads, with their respective ridges inobedience to the stresses of prehension, inclined proximally, and theseparticular ridges formed arches whose convexities were directed towardsthe base of the hand.At first the inclining of the pads by the stresses of prehension wouldthrow the ridges into a series of plain arches, it therefore appears that the“plain arch” is the most rudimentary of the patterns; later the morecomplex patterns were evolved as a result of the inclining of the pads withtheir associated subdermal ridges in the varying directions of the stressesof prehension.A “plain arch” pattern may be experimentally produced by layinglengths of cord in parallel rows across a cone of some plastic material,eg. modelling clay, and then shoving or dragging over the summit ofthe cone. The pieces of cord representing ridges will now be seen tobe drawn into arches, the degree of arching being proportional tothe amount of the stress of prehension, and the plain-arch pattern isproduced.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 anyone of these patterns, the ridges at the proximal end of the pattern, wherethe inclining of the pad was least, are disposed transversely, whereas at thecentre, where the inclining was greatest, the ridges are thrown into formscharacteristic of core centres ; and finally, from the centre to the distal end,where the inclining was intermediate in amount, the ridges are seen to bein arches successively more open. The subdermal ridges (fig. 2) did notyield under pressure to the same extent as the intervening shallowerportions of the epidermis, they were consequently more exposed to pressure,and as this caused them to hypertrophy, they came to be elevated in ribsabove the level of the surface (fig. 3); these ribs constituted epidermic ridges,and as they were moulded on the subdermal ridges, they produced a faithfulreplica of them and delineated the underlying pattern.“ Papillary ” Ridges and Patterns on the Volar Surface of the Hand 71BIBLIOGRAPHY.Gatton, Finger Prints, 1892.Hepsurn, Anat. Anz. Bd. xiii., No. 16, and The Scientific Transactions of theRoyal 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.