in children than in adults. In the latter they are best developed on the hands of persons who do a moderate amount of manual labor, and become less marked when the skin is thin and delicate, as in persons who do no manual work or protect their hands by always wearing gloves. They also become less marked by reason of pressure or wear on the hands of persons who have excessive manual labor to do and who have to handle bricks, lime and other substances, while that kind of employment is continued, but after it ceases they soon regain their natural condition, provided the skin has not been permanently injured.

The general direction in which the ridges and furrows run on the palm is sometimes transverse and sometimes oblique in long, wavy lines, but their continuity is often broken and frequently intersected by the crease lines, to which they bear no definite relationship. At the roots of the fingers these long, wavy lines are usually displaced and contorted by other systems of ridges and furrows being interposed, which run in different directions and form more or less definite patterns. On the digits the disposition of the ridges and furrows is transverse, or nearly so, except on the terminal phalanges, where the arrangement is very varied and generally more than one system of ridges occurs; here they are also grouped in such a manner as to form well marked patterns.

These ridges, which are not only to be found on the palmar surface of the hand, but also on the plantar aspect of the foot of both men and apes, are termed papillary ridges, from the relation they bear to the papillæ of the corium, which are arranged in serial rows underneath them. According to Kollmann each papilla has a body and two heads; the latter form the adjacent sides of two parallel ridges, while the intervening furrow corresponds with the cleft between the heads of the papilla. Outside each head is the duct of the sweat gland, which opens on the free surface at the apex of the ridge, while the distal side of each of the two ridges is formed by the adjacent heads of the next two papillæ. By taking the capital letter Y to represent a papilla with its body and two heads, and the letter I to indicate the sudoriferous ducts, a transverse section of

the groundwork of two ridges, their sweat ducts, and the adjacent side of the next ridge on either side of them may be diagramatically represented thus, ylyly. The completed ridges would be represented by a complex structural layer placed above and dipping down between the heads of the Y's but pierced by the I's, representing from below upwards the stratum Malpigii, stratum lucidum, and stratum corneum. The numerical distribution of the touch-bodies situated in the papillæ does not seem to be correlated directly with the degree of development or the fineness or coarseness of the ridges, because the former vary in number in localities where the latter are equally well marked. There is little doubt, however, that the ridges are intimately connected with and assist the sense of touch, though their precise relationship with it may be a matter of some speculation. The touchbodies being situated chiefly in the heads of the papillæ which project into the structure of the ridges, are thus prominently raised on the surface of the skin. They are consequently favorably situated for receiving impressions from objects touched or handled, not only by reason of their coming into contact with them, but also by the surface-area from which the impressions are conveyed to them being materially increased by the corrugations. Furthermore, the contact pressure between the skin of the finger and the object touched being greatest on the summits of the ridges and diminishing as the bottoms of the furrows are reached, a differential sensation is thereby produced which can not but be of immense value in increasing the perceptive and discriminating powers of the fingers with respect to the character of the objects touched. While the structure of the layers of the skin superficial to the papillæ and the ready response which the outermost of these make in becoming thicker and thinner, as well as harder and softer, according to the nature of the employment of the individual, affords the degree of protection to the sensitive organs underneath that is necessary under the varying external conditions to which the fingers are subject, and is of such a character as to admirably adapt it for collecting and transmitting sensations to them and ultimately

to the more distant nerve centres. In this connection also the subcutaneous tissues, consisting of fibrous trabeculæ crossing and interlacing in a complex manner and including more or less continuous lobules of fat constituting the stratum adiposum, which in the living body is a semi-fluid condition, play an important part by equalizing in all directions pressure of contact with outside substances and so favoring the perception of the stimuli thus produced by the nerve terminations. The ridges themselves discharge an important function relative to the act of grasping from the amount of friction they cause, and in this respect the roughness of the surface due to their presence is augmented by the fact that they raise the openings of the sweat-glands to a suitable height from which moisture can be distributed evenly to the surface of the skin and to that of the object grasped. On their efficacy in this connection may depend the directions and arrangement they assume in different parts of the hand as well as in the foot, but on the terminal phalanx the development of the nail has a considerable influence in elongating the form of the soft parts and in modifying their direction, particularly at the free extremity of the digit. Whether the patterns they assumed on the centre of the terminal phalanges are related in any way to the form of the eminences which exists there, appears uncertain, and still less can it be accepted that they are produced through lateral pressure between nascent structures.

The disposition and characters of the ridges and furrows may be studied by direct examination of the fingers, but it is much more convenient to do so from impressions of them taken on some suitable material. Model impressions may be taken on wax or collodion, which are very sharp and delicate, but for practical purposes impressions made on paper from fingers previously covered lightly with a thin layer of printer's ink are by far the most convenient and useful. By this method impressions which are permanent without further treatment can be quickly and easily made. This is therefore the plan usually adopted. But to get good impressions in this way a certain modicum of care and practice is needed. From the fact

that the skin has always upon its surface a certain amount of greasy excretion, the finger, when pressed upon a sheet of paper or other smooth surface, leaves behind it a portion of the excretion. If the finger be clean no mark of it will be visible to the naked eye, but a latent impression is nevertheless present, which can be readily developed by applying to it an impalpable powder, such as finely powdered plumbago or hydrargyrum cum creta (according as the surface bearing the latent impression is white or dark), which when moved over the impression will leave adhering to it a sufficient amount of this powder to make the ridges appear quite distinct, while the furrows are unaffected. The print will not be permanent unless subsequently fixed, but will be liable to be rubbed off or blurred by contact with other surfaces. This method has its uses, however, and does not entail any previous application of ink to the fingers to dirty them.

The apparatus required for ink impressions consists of a smooth plate of metal, glass, or porcelain, of about the size of a post-card; some printer's ink, of somewhat thinner consistency than is used by printers, which for convenience may be put in a collapsible tube, like that as artists' colors are treated; some sheets of white paper having a smooth, hard surface, and a roller such as is used by photographers and known as a squeegee, with which to distribute the ink on the plate. For the examination of the prints an ordinary reading glass, as well as a lens of about five cm. focal length, and on two needles mounted in handles, like those used in histological work, to serve as printers, are necessary. The various articles enumerated should be kept scrupulously clean and free from dust.

A

The following is the modus operandi of taking the impressions of the fingers: small quantity of ink is put on the plate and thoroughly rolled with the squeegee till the whole surface is equally covered with a thin layer. The fingers, having been previously washed and partially dried, are each rolled on the inked plate and then on the paper with the least possible pressure. In applying the fingers both to the plate and to the paper care should be taken to roll it from radial side of the nail over the pulp to the ulnar

side of the nail, so that the complete impression of the ridges of the whole of the terminal phalanx from one side to the other and from the transverse crease lines of the last joint to almost the end of the digit may be obtained. No halt must be made during the process of rolling the finger and it must not be permitted to slip, otherwise an imperfect or blurred impression will be the result. If the impression be not satisfactory the whole of the ink should be washed off the finger with benzine, and the process repeated. A good impression should show the ridges as black lines and the furrows as white spaces between them, clearly and sharply defined. If the lines representing the ridges are faint in color there has been too little ink on the plate; if, on the other hand, the lines are dark enough but the interspaces are not white and clear of ink, too heavy pressure has been put on the digit whilst rolling it, or there has been too much ink on the plate. It is essential that the furrows should be free from ink and only the tops of the ridges inked to get clear impressions. Having secured the impressions of the digits of a few persons it will be found on examining them that the arrangement of the ridges on the different fingers is subject to considerable variation in form and direction. Immediately above the crease-lines the ridges run transversely across the phalanx, while at its extremity they are curved in the form of an arch. On the central portion of the phalanx it may be found in some instances that they pass gradually from the transverse to the arched form, but in by far the larger number of cases they will be seen to assume several distinctive patterns. To this central part of the impression the greatest importance attaches, and in studying it particular attention must be given to the arrangement of the ridges forming it. The first one to systematically describe and classify the various patterns which occur on this portion of the digit was Purkenje in 1823, who divided them into nine different classes. Some subsequent writers have increased the number, while others have reduced them. It is now generally recognized that there exists three main types to which the different arrangements of the ridges met with conform generally, but there are several va

A

rieties of each type, and a few patterns are constituted by a combination of two types, or are of a nondescript form. fourfold division with certain subdivisions is therefore found to afford a sufficient classification for practical purposes. The several dispositions of the ridges are accordingly classified as Arches, Loops, Whorls and Composites.

The Arch is the simplest and most primitive arrangement of ridge met with. Fig. 1. It is formed by the ridges immediately beyond the crease-line of the last joint, which run in nearly straight lines across the phalanx, being succeeded by others which by degrees become more and more curved in the middle, till at last they assume the form of well-shaped arches, and as such the series is continued till the nail is reached. The degree of arching of the ridges and the progressive rapidity with which it occurs, varies in different fingers, but in no case do any of the ridges in their course from one side of the fingers to the other become twisted or turned. Fig. 1 is an example of an arch of ordinary form.

There is one variety of this type which is called the Tented-Arch. In it the more or less transverse ridges beyond the crease-lines are succeeded by one or more ridges, which suddenly become thrust upwards at an acute angle from the middle of the base of the arch, which causes the ridge immediately beyond to assume a tent-like shape. The upthrust ridges are not generally symmetrical, however, so that the arrangement has often a somewhat slanting appearance, which in some instances may make it look like a loop,

The Loop, Fig. 3, diagramatic, is the most common form of arrangement the ridges assume. The gradual transition of the ridges near the joint from the almost straight to the arched form which was found to obtain in the Arches, fails to be carried out, and a break occurs in the regular sequence, causing an interspace between the two series in the middle of the phalanx. The manner of formation of the interspace is important. The transverse ridges immediately beyond the crease-lines are succeeded by a ridge com

distance

across the axis line, and then descends a certain and passes away to the opposite side of the digit to that from which it came, without meeting the lower prong again, thus a gap is left here between the two prongs C and D, and a larger or smaller interspace in the middle of the phalanx. It often happens that

ing from one or other side of the digit, which suddenly forks at a little distance to the right or the left of the axis of the digit, Fig. 3A. The lower prong of

Fig. 4.

instead of a ridge forking as described two ridges which have hitherto run parallel suddenly diverge on one or other side of the digit, Fig. 4, the upper of the two

ridges ascending and curving so as to form an arch, while the lower one continues its more or less horizontal course to the opposite side of the digit, thus an interspace is left between them. In either case the point of the divergence there is formed the base and one side of a delta, Fig. 3x, the other side being completed by a short new ridge forming in the interspace. The delta thus formed is a very important landmark in this pattern, and is never present in arches. The ridges beyond the upper prong or divergent ridge forming the distal boundary of the interspace, are arranged in arches till the nail is reached. Turning now to the interspace, a new series of ridges are found to enter it by the gap, Fig. 3 C. D., left between the two prongs or ridges on the side of the digit opposite to the delta. By these and by independent ridges forming in the interior, the interspace becomes filled up so that no part of it is left devoid of ridges. On tracing this new series of ridges it will be found that in the middle of the gap a ridge from that side of the digit passes into the interspace for a certain distance and then turns round, that is to say doubles round on itself without twisting, and runs again through the gap by which it entered. There may be only one ridge which thus doubles round and forms a loop. More frequently there are several ridges arranged in series round this centre or staple-like loop, some of which pass in and out on either side of it through the gap, but many of them only curve round it in the interspace. The independent ridges filling the rest of the interspace are straight or curved, are of varying length. The top of the central ridge, like the delta, is an important point, because as the outer terminus of the interspace is marked by the outer angle of the delta, so the inner terminus or the point of the core is situated at the top of the ridge farther from the delta, where it begins to bend on itself to form the top of the staple-like end of the loop. These are two fixed points in the pattern between which the number of ridges may be counted and from which the rest of the pattern may be surveyed. Certain variations of the core are not unfrequently met with which require notice. The core may appear as two central ridges which terminate abruptly, or there may

be three terminal ridges round which the first of the series of ridges loops. In the former case the two central ridges are considered as the central loop, with the end defective and the point of the core is the top of the more distant of the two ridges from the delta, but in the latter case the top of the central ridge is taken as the inner terminus, the other two rodlike ridges situated one on either side of it being regarded as the legs of the central loop, the arched end of which is incomplete. In counting the number of ridges in a loop pattern the enumeration is made along a straight line from the outer terminus to the inner terminus, but the ridges on which the terminuses are situated are not included, only the ridges between them being counted. The degree of slope shown by loops varies very much in different fingers. In some it approaches the horizontal, while in others it is nearly vertical.

The direction of their slope, which is determined by the position of their proximal ends, may be to the right or to the left side of a digit, but it must be remembered that the slope of similar loops will be in opposite directions on the right and left hands. When the distal and closed end or top of the loop is on the same side of the hand as the thumb and the open proximal end opens on the little finger side of the hand it is called an Ulnar loop. When the closed top of the loop is on the little finger side and its open proximal end is on the thumb side it is called a radial loop. According then as the open mouth of the loop is situated on the ulnar or the radial side of the hand so is the loop named. It is alsò important to remember when looking at the impression of a finger bearing the loop that the direction of the loop appears as the reverse of what it is when the finger itself is examined, and that to determine whether the impression of a single digit with a loop pattern upon it is of the ulnar or radial variety it is essential to know whether the print is that of a right or a left hand digit. Several varieties of form are met with in loops, thus some of the core loops are sometimes found to meet either an enveloping loop or the boundary ridge of the interspace at an angle, they are sometimes slightly deflected downwards at the closed end, or the central