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Anatomical and microscopic study of the volar dermal ridges of the rat (Rattus norvegicus).

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Anatomical and Microscopic Study of the Volar Dermal Ridges of
the Rat (Rattus norvegicus)
Department ofForensrc Medzczne, Tokyo MedLcal and Dental Unluerslty,
Ybhirna, Bunkyeku, Tokyo 113, Japan
Dermatoglyphics,Dermis, Rat
The epidermal ridges of the rat (Rattus norvegicus), which are
distributed only on the volar pads and digital apices, were studied. Examination of the ridges was difficult on the epidermal surface, as the undulations
expressed on the epidermis are weak. Therefore, the dermal surface, prepared
by alkaline solution treatment, was inspected by scanning electron microscopy
and staining with toluidine blue. The dermis of the pads and digital apices is
composed of ridged and rippled areas. The ridged area, where sweat ducts are
distributed, is constructed of grooves and ramparts. Frequently, the sweat duct
is surrounded by a dermal collar, and the groove is separated by a dermal
partition. The grooves and ramparts display dermatoglyphic configurations,
such as whorls, loops, cusps, triradii, and some other patterns, which are peculiar to each pad and digital apex and comparable to dermatoglyphic patterns
of man and other primates.
The occurrence of epidermal ridges at the
palmar and plantar surfaces is common in
the primates, including the human species.
On the other hand, this characteristic appears sporadically in other mammals and has
been reported in some species of rodents,
marsupials, and carnivores (Merkel, 1880;
Klaatsch, 1888; Whipple, 1904; Dankmeijer,
1938; Cummins and Midlo, 1943). In the rat
(Rattus noruegicus), undulations of the ridges
are not sufficiently developed at the volar
surface to be clearly identified with the naked eye. No systematic studies have been
undertaken on the ridge arrangement in the
rat, except for brief descriptions of the existence of a ridged structure by Merkel (1880)
and Klaatsch (1888). Okajima (1975a) reported a technique that enables one to inspect the ridge arrangement at the dermal
surface, and, at the same time, he presented
dermal ridges of some animals including the
In this paper, we describe the anatomical
structure of the epidermal ridges of the rat
and its dermatoglyphic features by applying
the above-mentionedtechnique.
0 1985 ALAN R. LISS, INC.
About 700 adult and infant rats were collected for this study from several inbred
strains reared in the National Institute of
Genetics CMisima) and some conventional
strains from animal dealers.
Cast of the epidermal surface
The volar epidermal surface of sacrificed
rats was cleaned with ethanol, and a cast of
volar pads and digital apices was prepared
with silicone rubber.
Pads of the palm and sole were taken from
adult rats and fixed in buffered formalin.
After the specimen was embedded in celloidin, sections, 30 pm in thickness, were cut
and stained with hematoxylin and eosin.
Preparation of the dermal surface
The original preparation technique (Oka$ma, 1975a, 1979)was modified in this study.
Received August 30,1984; revision received January 21,1985;
accepted January 31,1985.
The hands and feet were separated from the
body proximal to the wrist and foot joints,
fixed in 10% formalin, and incubated in 1 N
potassium hydroxide solution at 30°C for 2
or 3 days. Then the specimens were washed
in running water for 2 days. Usually, most of
the epidermal tissue was separated from the
dermis by this treatment alone. The remaining epidermal tissue was removed mechanically by slight touch with a cotton swab or a
brushlike terminal of a thread. At this manipulation, the specimen was stained with
0.05% toluidine blue solution, so that the
dermal surface and the epidermal tissue remaining on it were easily identified.
Staining of the dermal surface
The dermal surface thus exposed was
stained with 0.05% toluidine blue solution
for about 20 seconds, rinsed in water, and
placed in a dish of water. The stained dermis
was inspected under a stereoscopic microscope and photographed. The hand and foot
were fixed in an extended position on a rubber plate with rubber strings at the proximal
site and at the phalanges.
When the examination was finished, the
reagent was removed from the tissue by immersion in 70% ethanol and then the ethanol
was replaced by water. After this, the specimen was preserved in 10% formalin, and, if
necessary, the inspection was repeated using
the same procedure.
Scanning electron microscop,y (SEM)
After the stained dermal surface was examined, pads and digital apices were taken
from several rats. The specimens were
washed in distilled water, postfixed for 2
hours in 1.5% osmium tetroxide, dehydrated
through a graded series of ethanols into isoamyl acetate, and dried in a pressure chamber by the critical point procedure. The specimen was fixed, dermal surface up, to a n
aluminum stub with silver conducting paint,
coated with evaporated platinum, and viewed
with an Hitachi S-700 operated a t 20 kV in
the secondary electron mode.
Observation of the epidermal surface
First, we examined the epidermal surface
of the volar pads and digital apices of adult
and infant rats with a magnifying glass and
under a stereoscopic microscope. On the epi-
dermal surface, the ridged structure was recognized in various grades of expression.
However, the undulations and contrast were
usually weak, and the ridges were, in most
areas, not discernible, so that it was almost
impossible to confirm the entire ridge arrangement with the naked eye. Attempts to
take dermatoglyphic prints by the usual
printing methods were not successful, as the
furrows were too shallow.
Following this, the epidermal surface was
examined on the silicone rubber casts. The
relief of the ridges was more clearly seen
under a stereoscopic microscope than was the
epidermis itself. However, the degree of
expression was different from pad to pad and
from site to site as well as from animal to
animal. Moreover, the surface was frequently smooth, and the ridges were not visible, especially in the infant rats. Therefore,
precise identification of ridge configurations
was usually difficult. However, it was determined that the pores of sweat ducts are arranged on the midline of the epidermal ridge.
Surface structure of the dermis
The dermal surface of the volar pads and
digital apices was examined by the scanning
electron microscopic (SEMI procedure. The
surface is characterized by two morphologically dissimilar areas, i.e., the ridged and the
rippled, as defined by the different morphological features of the dermal undulations.
Generally, the ridged area is localized in the
higher part of the pad and digital apex, while
the rippled area is located peripheral to the
ridged area, usually in the lower region. As
the SEM picture shows (Fig. 11, the dermal
surface presents wavelike undulations that
are constructed of alternate arrangements of
dermal grooves and ramparts in the ridged
area. The groove is a deep, linear depression
of the dermis, where sweat ducts lie. The
orifice of the sweat duct presents a deep, funnel-shaped cavity at the dermal surface.
In the rippled area, the dermal surface is
constructed of papillalike projections and
lower folds. Some of them are arranged linearly, but others are distributed more or less
in a n irregular image.
The basic difference between the two areas
is the presence of sweat ducts in the ridged
area, and their absence in the rippled area.
The groove corresponds anatomically to the
epidermal ridge and the rampart to the epidermal furrow (Fig. 2). The sweat duct penetrates the stratum corneum of the epidermis,
Fig. 1. Dermal surface of the first interdigital and
thenar pad on the right palm of a rat (SEMI. The ridged
area (Rig) is represented by an alternate arrangement of
the groove (GI and the rampart (R). Sweat ducts (SD) are
frequently surrounded by a collar (C) of dermal projec-
tion. The groove is frequently compartmentalized by a
dermal partition (PI. The rippled area (Rip) is constructed of papillalike projections and lower folds of the
forming a spiral, and opens at the summit of
the epidermal ridge. However, it often opens
at a flat surface, because the ridged structure
is not manifested. Superficial to the rippled
area of the dermis, the epidermal surface is
smooth, and the epidermal tissue is generally somewhat thinner than in the ridged area.
In the ridged area, the groove is frequently
modified by a n irregular occurrence, bifurcation, or conjunction of the ramparts. Sweat
ducts are not evenly distributed in the
groove. They are arranged closely in some
grooves but are almost absent in others. The
groove is usually narrower a t the site where
there is no sweat duct. Moreover, the groove
looks rudimentary and like a mere fissure
where the ramparts lie closely parallel.
The orifice of the sweat duct is frequently
surrounded by a dermal collar, a cylindrical
or a semicircular projection of the derms. In
addition to the sweat ducts, the groove is
frequently punctuated by low dermal partitions, which are elevated from the base and
usually extend across the groove, independent from, or adjacent to, the sweat duct (Fig.
The summit of a rampart forms a single
edge and is fairly smooth along its long axis
in many rats, while in others it is fringed
with small dermal projections, presenting a
serrated appearance (Fig. 3). This characteristic appearance was observed on each pad
and in both adults and infants. The formation of the dermal furrow a t the rampart,
Fig. 2. Histological presentation of the epidermal
ridges of the rat (hematoxylin and eosin, x 60). The
section was cut parallel to the long axis of the second
interdigital pad of a right foot and perpendicular to the
ridges. Weak undulations of the epidermal surface pres-
ent epidermal ridges (ER) and furrows (EF). The dermd
surface is constructed of grooves (G) and ramparts (R).
Ducts (SD) of sweat glands (SG) penetrate the dermis
(Der) and the epidermis (Epi) and open at the summit of
the epidermal ridge.
which is a common characteristic of man and
other primates, was not detected in the rat.
Though the appearance of the groove and
the rampart is modified by many factors as
stated above, their alternate arrangement
displays a definitive ridged structure on the
dermal surface that is comparable to the dermal ridges of the primates.
Dermatoglyphic inspection
by the staining method
The dermal surface stained with toluidine
blue presented in Figure 4 is from the same
specimen as shown in Figure 1. This specimen was first stained and examined and then
used for the SEM examination. The dermal
projections of the ridged area stained with
toluidine blue in a violet tone, while the
groove remained unstained (Fig. 41, in the
same manner as the dermal papillae of man
and other primates.
Every rampart, collar, partition, and fringe
in the ridged area and the dermal papillae
and folds in the rippled area, which are demonstrated in the SEM picture (Fig. 11, coinFig. 3. Fringe formation of the rampart (SEM). Hypothenar pad of a left hand. The edge of the rampart
presents dermal projections arranged in a serrated
cide exactly with the image displayed by the
staining method (Fig. 4).Thus, the staining
procedure permits easy identification of the
arrangement of the ridges.
Examples of dermatoglyphic perspectives
of a palm and a sole are provided in Figures
5 and 6. As these pictures show, each pad
and digital apex presents a particular ridge
arrangement. The simplest and most common type is that in which the parallel ridges
lie transverse to the long axis of the pad
elevation. This type appears on most pads.
A triradial ridge arrangement appears frequently on the first interdigitallthenar and
the second to fourth interdigital pads on the
palm, and on the third and fourth interdigital pads on the sole, occasionally accompanied by some particular pattern formation.
The third interdigital pad of the palm is a
very striking area where the ridges present
abundant configurations, i.e., triradii, whorls,
loops, cusps, and some other types of patterns
(Fig. 7), which are similar to the dermatoglyphic patterns on the digital apex, palm,
and sole of the primates. On the digital apex,
although the size of the patterns is small,
Fig. 5. Dermal surface of a left palm (toluidine blue
ridge arrangements characteristic to each staining).
Ridged structure is recognized on the first (I),
digit were observed.
second a),
third (III), and fourth (IV)interdigital pads,
and the thenar (Th)and hypothenar (Hy) pads. On the
third interdigital pad, a whorl pattern is observed. Digits are represented by Arabic numerals.
It has long been known that all the members of the primate order and some species of
rodents, carnivores, and marsupials possess
friction skin. Whipple (1904) made an extensive survey of epidermal ridges in mammals.
Dankmeijer (1938) undertook a systematic
study of marsupials, reporting the existence
of dermatoglyphic traits in some species of
this order. Cummins and Midlo (1943)presented a review of dermatoglyphic traits in
animals including those other than the primates. But none of these authors mentioned
the presence of epidermal ridges in the rat.
However, the existence of ridged structures
on the volar skin of the rodents had been
reported by some earlier workers. Merkel
(1880) first described it in the squirrel and
the rat. His statement about this characteristic in the rat was later quoted by Klaatsch
(1888) as follows: “He (Merkel) found with
the naked eye that the pads present a striped
surface that reminds one of the finger apex
Fig. 4. Dermal surface (toluidine blue staining). This of man. When the epidermis is removed by
picture was prepared from the same specimen as shown
in Fig. 1. Details of the dermal structure illustrated here maceration, the stripe is conditioned by papillary ridges as is found at the nail bed of
coincide with those of the SEM image.
Fig. 6. Dermal surface of a lefi sole (toluidine blue staining). Ridged structure is recognized
on the pads. For abbreviations, see Figure 5.
man. These are carriers of numerous tactile
Subsequently, Whipple (1904)described the
configurational arrangement of ridges on the
voIar pad of the Neotoma (wood-rat) among
the rodents and stated “The highest part of
each pad is covered by somewhat broken
ridges separated by deep furrows. The more
elevated pads, such as the apical and the
hypothenar of the hand, show a n approximately concentric arrangement of ridges,
while upon other pads the arrangement is
transverse.” In her sketch of a section perpendicular to the ridges, she presented the
duct of sweat glands opening between ridges
on the epidermal surface, In this illustration,
remarkable undulations are demonstrated
both a t the epidermal surface and the dermoepidermal junction, the epidermal furrow
anatomically corresponding to the dermal
groove and the epidermal ridge to one or two
rows of dermal papillae.
Contrary to her findings, it was observed
in the present study that the orifice of the
Fig. 7. Representative pattern types on the third interdigital pad of the palm (toluidine blue
staining). a. loop. b. cusp. c. triradius. A whorl pattern is demonstrated in Figure 5.
sweat ducts is not located in the furrow, but
on the midline of the epidermal ridge. In
addition, though the undulations at the epidermal surface are often indiscernible, histological sections showed that the epidermal
ridge anatomically corresponds to the groove
and the epidermal furrow to the rampart,
and that the sweat duct opens at the summit
of the epidermal ridge, as is the case among
It was confirmed in this study that the
dermal surface of the volar pad and the digital apex is composed of two distinct regions,
i.e., ridged and ripple areas, as defined by
the presence or absence of sweat glands. The
ridged area consists of an alternate arrangement of dermal grooves and ramparts, similar to that observed in the early developmental stage of human fetuses (Okajima,
1975b, 1982). Thus, the dermal furrow, as
observed in fully developed primates, is absent in the rat. It is possible that the less
complex morphology of the rat is associated
with a weak expression of the epidermal
Whipple (1904) mentioned that there are
no epidermal ridges in those rodents (Mus,
Microtus, etc.). However, she presented in her
sketch that the epidermal ridges of the woodrat are markedly elevated. Therefore, the
expression of the epidermal ridges is different between species in the rodents, and further morphological findings are needed to
understand the difference.
On the other hand, it is characteristic of
the rat that the dermal surface is modified
by formation of partitions and collars of sweat
ducts and a somewhat irregular arrangement of ramparts. These dermal structures
are revealed by both SEM and staining pro-
cedures. In spite of these modifications, the
groove maintains its linear nature and, as a
whole, presents a configurational arrangement that can be defined as a dermatoglyphic trait.
We have found that the ridge arrangement
characterizes each volar pad. In some areas,
such as the third interdigital pad of the palm,
configurations quite comparable to the dermataglyphic patterns of man and other primates were observed.
The staining method is practical for the
dermatoglyphic analysis. We have revised
the original preparation technique (Okajima,
1975a, 1979)by applying 1 N potassium hydroxide solution for 2-3 days at 30" C . By
this procedure, the epidermis of the specimen
can be easily and completely removed, resulting in a specimen of good quality.
Primates have been considered to be the
only laboratory animals available for dermatoglyphic study. However, there are limitations in the use of primates, such as their
extremely high cost, the small number of
animals available, long gestational periods,
and the difficulty in obtaining precisely
timed conceptions. The results presented here
confirm that it is possible to use the rat, a
conventional laboratory animal, as an experimental model for dermatoglyphic study.
We are indebted to Mr. H. Miyamoto for
technical advice in SEM preparation. This
study was supported by a Grant-in-Aid for
Scientific Research No. 57570238 from the
Ministry of Education, Science, and Culture
of Japan.
Chacko, LW, and Vaidya, MC (1968)The dermal papillae
and ridge patterns i n human volar skin. Acta Anat.
Cummins, H, and Midlo, C (1943)Finger Prints, Palms
and Soles. Philadelphia: Blakiston.
Dankmeijer, J (1938) Zur biologischen Anatomic der
Hautleisten bei den Bcuteltieren. Morph. Jahrb.
Klaatsch, H (1888)Zur Morphologie der Tastballen der
Saugethiere. Morph. Jahrb. 14t407-435.
Merkel, F (1880) h r die Endigungen der Sensiblen
Nerven in der Haut der Wirbelthiere. Rostock Verlag
der Stillerschen Hof.
Okajima, M (1975a) Technical aspects of dermatoglyphic
examination in primates. In S Kondo, M Kawai, and
A Ehara (eds): Contemporary Primatology. Basel: Karger, pp. 49-53.
Okajima, M (197513) Development of dermal ridges in the
fetus. J. Med. Genet. 12t243-250.
Okajima, M (1979) Dermal and epidermal structures of
the volar skin. Birth Defects Orig. Art. Ser. 15(6):179198.
Okajima, M (1982) A methodological approach to the
development of epidermal ridges on the dermal surface
of fetuses. Prog. Clin. Biol. Res. 84t175-188.
Whipple, IL (1904) The ventral surface of the mammalian chiridium. Z.Morph. Anthropol. 7t261-368.
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volar, stud, microscopy, rat, anatomical, norvegicus, rattus, dermal, ridges
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