lower forms the transition stages from simple epidermic structures such as warts and rings to fully formed ridges occurs in the regions which are less exposed to pressure, suggested the possibility of finding in the narrow transition area between the ridged region and the skin of the dorsum, especially in embryos, some suggestion as to this process. As the elevation of the ridges is due largely to the rather late development of the stratum corneum, it was difficult to find a stage which was sufficiently advanced to render the ridges distinguishable externally and which would at the same time show the simpler epidermic structures. An advanced human fetus

L

FIG. 5.

proved the most satisfactory for this purpose, and the best results were obtained from the transition region along the sides of the middle phalanges. Fig. 5 shows a camera drawing of a surface preparation of the epidermis of this region. Upon the side of the digit the orifices of the sweat glands are wide and each is surrounded by an elevated rim of the stratum corneum, the whole structure being that of an epidermic wart. These warts appear, however, to be arranged in rows, and the drawing shows a rapid transition from separate warts to ridges, one feature of this transition being the increased length of the coiled ducts of the sweat glands and a lateral compression of their orifices. Except that the transition is a narrow one, the process of ridge formation differs in no particular from that of Midas lagothrix. Moreover these warts having been demonstrated in the embryo, it seems safe to conclude that the little separate elevations continuing for a short distance the course of the ridges in the transition regions of the adult skin, usually particularly well seen upon the inner side of the terminal phalanx of the second finger (Fig. 6a), are actually primitive warts, examination with a lens demonstrating the opening of a sweat gland in the center of each. In some cases these warts seem to be grouped or fused into rings suggesting the conditions in Didelphys and Lemur; usually, however, they occur singly. The very frequent occurrence of "islands" in the primate friction-skin also suggests the development of ridges phylogenetically from separate components (Fig. 6b).

Three monkey embryos, one an Alouatta, the other two Platyrrhine forms (species undetermined), showed along the edge of the friction-skin similar transition stages from warts to ridges.

Concerning the function of the epidermic ridges (Part II.,

Sec. D), after extended observations and discussion, the investigator says:

The general principles, then, which are involved in the function of ridges are:

1. That the function is primarily to increase resistance between contact surfaces for the purpose of preventing slipping, whether in walking or in prehension.

2. The direction of ridges is at right angles with the force that tends to produce slipping, or to the resultant of such forces when these forces vary in direction.

3. The shape of the pad elevation, the direction of flexion, and the direction of motion are the factors determining the direction of the slipping force, and therefore the direction of the ridges.

Again, "Incidentally the ridges acquire an important tactile function."

In Part III., Sec. C, is discussed Modified Primary Patterns; the various types of modification, and their probable cause,

although in doing so it must be borne in mind that a single type of pad modification seldom occurs unaccompanied by others. We may consider these types, however, to be four in number:

1. Failure of divergents, resulting in triradii becoming extra-limital or obliterated. (See Fig. 7a and b.)

2. Reduction of pads, resulting in degeneration of triradii.

3. Flattening of pads, resulting in a deviation from the concentric arrangement of ridges upon the pad area.

4. Fusion of pads, resulting in the coalescence and in the exclusion of triradii.

FIG. 7. Two apical graphs in which (a) one triradius has become extra limital, and the other nearly so; in (b) both triradii have become obliterated. In each case accessory degeneration triradius" has developed in connection with a loop formation. At the extreme lower corners unit ridge elements may be seen.

an

Continuing, and referring to group (2), Miss Whipple says: The modification of patterns which are due to pad reduction are probably the most frequent of all pattern modifications. As reduction has pro

FIG. 8.

ceeded farther in man than in most monkeys (excepting the Anthropoids) we may select from different individuals of the human species cases which illustrate every step in the process. The series given in Fig. 8 show how, in the apical pads, beginning with the slipping of one or both of the embracing radiants of one triradius within those of the other, a variation involving at first only a few ridges (b), one triradius may approach

nearer and nearer to the center of the pattern (c, d, e), its radiants embracing fewer and fewer concentric ridges until the triradius finally suffers complete degeneration, leaving the pattern known in Galton's terminology as the "loop" (f) which has only one triradius, the loop opening in the direction of the divergent of the triradius which has degenerated. Again, by a similar series of minute variations, this remaining triradius may approach more nearly to the middle of the pattern, until the loop involves but a single ridge, from which condition it is only a step through Galton's "tented arch" to the "simple arch" in which the last vestige of the second triradius has disappeared. These transition forms in the apical patterns were fully recognized and described by Galton as constituting a slight obstacle to a perfectly systematic classification of fingerprints. . . . It should also be noted that there may occur a simultaneous approach of both triradii to the center of the pattern, the pattern remaining typical in form but reduced in size.

This type of modification is then traced in palms and soles. Under group (3),

Types of pattern modification which are due to a flattening of the pad, a condition which is in some instances correlated with reduction, and in others with extension of the pad area. With the change of pressure upon a pad naturally accompanying such a change of form, very decided modifications in the disposition of ridges occur leading in the direction of the establishment of parallel straight ridges, such as we would expect to find upon a flat surface. The flattened, reduced apical pads both of man and of a few of the monkeys were found to illustrate one very common method of attaining this end. It will be seen from the series shown in Fig. 9 that

this line of variation may begin by the displacement of only a few ridges at the center of the pattern, the result being the establishment of a spiral rather than a perfectly concentric pattern. Following this may come a greater and greater amount of variation from the concentric arrangement until a double loop (vortex duplicatus of Purkinje) or even an S-shaped figure is formed. In rare cases more often seen in the apical patterns of the human foot and in the proximal patterns this line of variation has proceeded so far that the pattern has become separated into distinct loops and an accessory degeneration triradius is introduced (see Fig. 7a and b), that is a triradius not originally present in the typical scheme but formed incidentally in the process of degeneration of the pattern.

Modifications from this same cause occurring in the palms and soles are then considered at considerable length and in great detail.

From this brief biological review it will be seen that any friction-skin impression or dermatograph is really much more than a record of merely external epidermic characteristics, for these features are in turn conditioned upon internal tissue structure of the dermis, the configuration of which is determined and fixed during early embryonic life, and is therefore capable of being associated with but a single individual. Except for a change of size proportional to the growth of the bodily parts, or changes acquired during postembryonic life by external causes such as deep cuts or burns, or from disease of the tissue evidenced by a felon, boil, etc., the configuration remains unchanged through the individual's life.

What then is required to establish an identification; what is the process; how do these biological or anatomical conditions. satisfy the requirements?

For guidance, let us consult an authority22 on the principles of identity evidence:

. . . In the process of identification of two supposed objects, by a common mark, the force of the inference depends on the degree of necessariness of association of that mark with a single object.

For simplicity's sake the evidential circumstance may thus be spoken of as "a mark." But in practise it rarely occurs that the evidential mark is a single circumstance. The evidencing feature is usually a group of circumstances, which as a whole constitute a feature capable of being associated with a single object. Rarely can one circumstance alone be so inherently peculiar to a single object. It is by adding circumstance to circumstance we obtain a composite feature or mark which as a whole can not be supposed to be associated with more than a single object. The process of constructing an inference of identification thus consists usually in adding together a number of circumstances, each of which by itself might be a feature of many objects, but all of which together can conceivably coexist in a single object only. Each additional circumstance reduces the chances of there being more than one object so associated.

Continuing, he says, in discussing the terms identity, alike, similar, and resemblance:

We remember to have read in a judgment of the Indian High Courts (unfortunately we can not now give the reference) that the judges considered the case was not proved because the evidence only established likeness and not identity. . . . terms such as "exact likeness," "precise similarity" are misleading. For as soon as you have removed all internal difference and resemblance is carried to such a point that perceptible [material] difference ceases, then you have identity. As soon as you begin to analyze resemblance you get something else than it; and when you argue from resemblance, what you use is not the resemblance, but the point of resemblance, and a point of resemblance is clearly an identity.23

22 John H. Wigmore, "Principles of Judicial Proof, General Principle of Identity Evidence."

23" Principles of Judicial Proof," John H. Wigmore, Little, Brown & Co., Boston, Mass., 1913, pages 64-67.