Received: 5 July 2020
Accepted for publication: 12 November 2021
Slov Vet Res 2021: 58 (4): 147 – 53
DOI 10.26873/SVR-1356-2021
UDC 599.742.734:591.421:572.7:591.8
Original Research Article
Introduction
The Euroasian lynx (Lynx lynx) is an endangered 
species of wild animal (1). The species features of 
the lynx are medium size, a small head, a prominent 
ruff of fur, ears tipped with tufts of black hair, and 
long legs relative to its body length. The literature 
reports that the most distinguishing anatomical 
characteristic of these wild animals is the absence 
of a set upper premolar (2).
The planum nasale, which comes from a Latin 
word meaning the tip of the nose, is a well-studied 
anatomical and histological structure in various 
MORPHOLOGY AND HISTOLOGY OF THE EURASIAN LYNX (Lynx lynx) 
PLANUM NASALE
Hasan Hüseyin Ari1,3, Sema Uslu2*  
1Departments of Anatomy, 2Departments of Histology and Embryology, Faculty of Veterinary Medicine, Sivas Cumhuriyet University, Sivas, 
Turkey, 3Departments of Anatomy, Faculty of Veterinary Medicine, Kyrgyz-Turkish Manas University, Bishkek, Kyrgyzstan Republic
*Corresponding author, E-mail: semauslu43@hotmail.com
Abstract: This study reveals the macroscopic and microscopic structures of the Eurasian lynx planum nasale using materials 
from three dead females obtained from the Sivas Forestry Branch of Agriculture and Forestry Ministry of the Republic of Turkey. To 
accomplish the purpose, planum nasale was investigated using macroscopic, histological, and scanning electron microscopy 
(SEM) techniques. The microscopic examination showed that the planum nasale consists of hairless, moist, glabrous skin and 
resembles a ship anchor with arm, palm, stock, and sickle parts. The planum nasale’s surface is formed by epidermal plates or 
epidermal ridges, which  were separated from each other by primary and secondary fissures showed in SEM and macroscopic 
figures. Based on the microscopic examination, the Mercel’s cells and nerve ends are located in the basal sheet of the planum na-
sale’s epidermal layers. In addition, the pores situated on the surface of the epidermal ridges and the dense connective bundles 
were settled in the dermal layers, based on the SEM examination.
Key words: Eurasian lynx (Lynx rufus); morphology; nasal plane; planum nasale
species (3, 4, 5, 6, 7). This anatomical structure 
is called the nasal plane (planum nasale) in 
carnivores and small ruminants but the nasolabial 
plane (planum nasolabiale) in large ruminants 
and the rostral plane (planum rostrale) in swine. 
The nasal plane is macroanatomically formed 
by glabrous skin and philtrum, different from 
other regions of the head (8, 9, 10, 11). The skin 
of the nasal plane includes medial nasal wings, 
which are differentiated for adaptation to different 
environments. The surface of the nasal plane 
skin exhibits a unique morphology that includes 
papillae or epidermal ridges (4, 5). The anatomical 
structure consists of the epidermal ridges, which 
are used as a nasal print (5, 12) because of the 
individual animal’s characteristics throughout 
H. H. Ari, S. Uslu148
life (13, 14). Histologically, the planum nasale’s 
skin consists of an epidermis and a dermis. In 
addition, Esrah (5) reported that skeleton muscle 
exists just below the dermis.
The morphology of the planum nasale has been 
compared between various species for many years. 
Despite several current studies on the anatomical 
structures of the Eurasian lynx (1, 15), to our 
knowledge, no anatomical descriptions of the 
nasal plane in the Eurasian lynx are available, 
so this study could present the first anatomical 
findings on the planum nasale obtained using 
light and scanning electron microscopy.
Materials and methods
Gross anatomy 
The three female Eurasian lynx used in this 
study died from natural causes (cadaver I was 
6,9 kg, cadaver II was 7,6 and cadaver III was 
7,2 kg in weight, respectively). The animals were 
obtained from the Republic of Turkey Ministry 
of Agriculture and Forestry (Sivas branch) and 
were immediately transported to the Anatomy 
Department of the Veterinary Faculty of Sivas 
Cumhuriyet University (16). Then, we bilaterally 
inserted a plastic cannula into their common 
carotid artery and cleaned the arterial system 
of each cadaver with hydrogen peroxide and 
water solution. We fixed the cadavers with a 10% 
formalin solution administered via the plastic 
cannula. The planum nasale of each cadaver was 
photographed with a Canon EOS 50D camera. 
The nomenclature used in this study was adopted 
from the Nomina Anatomica Veterinaria (17).
Light microscopy 
The tissue samples were fixed in buffered 
formalin for 24 hr, dehydrated in graded alcohol, 
and embedded in paraplast to create blocks. 
Serial sections were cut at 5–6 μm thickness. 
The sections were stained with a modified version 
of Mallory’s triple stain for general histological 
examination (18). 
Scanning electron microscopy 
The specimens collected from the planum 
nasale samples were washed in distilled water 
and 2.5% glutaraldehyde three times (10 min 
each), dehydrated in an ascending series of ethyl 
alcohol solutions (50%, 70%, 90%, and 100% 
alcohol), dried until they reached the critical point 
using liquid carbon dioxide, and mounted on 
metal stubs. The samples were coated with a gold-
palladium alloy using a sputtering device; then, we 
examined and photographed the specimens with 
a scanning electron microscope (Zeiss, Germany) 
(10kV) at the Advanced Technology Research 
Centre of Sivas Cumhuriyet University, Sivas (19).
Ethical Statement: This study was approved by 
the Republic of Turkey Ministry of Agriculture and 
Forestry (Sivas branch) (09.08.2018-72784983-
488.04-176382).
Results
Gross morphology 
The planum nasale of the Eurasian lynx is 
located around the two nostrils and the middle 
area of the upper lip. Its skin surface is hairless, 
glabrous, moist, and grayish-black, and it has a 
dermatoglyphic pattern consisting of epidermal 
ridges (see Figure 1). It was divided by a philtrum 
into two equal halves, around the nostril and only 
the middle area of the upper lip (see Figure 1). 
The planum nasale of Eurasian lynx was in the 
form of a sketchy ship anchor shape consisting 
of arm, palm, shank, stock, and shackle parts 
(see Figure 1A). The arm of the ship anchor was 
directed to the dorsum nasi, while the shank 
was directed toward the ventral of the planum 
nasale. The arm of the planum nasale (the arrow 
in Figure 1A) is located dorsally to the tip of the 
nose, while its palm (“Pa” in Figure 1A) is situated 
at the dorsolateral wings of the nose, directed 
medioventrally. A black dorsal border (the arrow 
in Figure 1A) was evident between the hairy skin 
of the dorsum nasi and the arm of the planum 
nasale. The dorsal border of the planum nasale’s 
arm was concavely directed toward the dorsum 
nasi. The width of the planum nasale arm dorsally 
supported the nostril (“Ns” in Figure 1A) and 
was wider than the planum nasale’s palm. The 
planum nasale’s palm (“Pa” in Figure 1A) on both 
sides situated the lateral wings of the nose and 
the dorsolateral of the planum nasale. The width 
of the planum nasale’s arm dorsally surrounding 
the nostril was wider than the planum nasale’s 
Morphology and histology of the Eurasian Lynx (Lynx lynx) planum nasale 149
palm. The planum nasale palm on either side was 
situated around the lateral wings of the nose and 
dorsolateral limited the nostrils. The lateral border 
of the convex planum nasale palm firstly began 
from the dorsal side of the nostril, then continued 
to the medial side, and finally ended at the ventral 
side. The lateral and dorsal borders of the planum 
nasale and philtrum (arrowhead in Figure 1A) 
were dark-colored glabrous skin, unlike the arm, 
which comprises glabrous light-colored skin in the 
central portion planum nasale’s arm. The planum 
nasale’s shank (“Sh” in Figure 1A) is situated in 
the area between the left and right nostrils. The 
philtrum (the arrowhead in Figure 1A) extended 
from the dorsal midline of the planum nasale’s 
shank to the planum nasale’s shackle and upper 
lip. The planum nasale’s stock (“St” in Figure 1A) 
is located mediolaterally in the ventral portion of 
the planum nasale, and the ventral part of the 
planum nasale shank narrows dorsally to the 
upper lip to become the shackle of the planum 
nasale (“Shk” in Figure 1A). The skin of the planum 
nasale’s shackle and the upper lip was dark and is 
divided into two equal halves by the philtrum. The 
glabrous skin surfaces of the planum nasale have 
many moist dermal protuberances and grooves 
Figure 1A: The macroscopic view of Eurasian lynx Pla-
num nasale. (A) A photograph of the planum nasale’s 
anatomical structures: the arm (Ar), palm (Pa), and 
dorsal border of the planum nasale (arrow); the nostril 
(Ns); the philtrum (arrowhead); the shank (Sh); and the 
shackle (Shk) and stock of the planum nasale (St)
(the star in Figure 1A), which were wider and 
darker in the central area of the planum nasale 
than at the edges of the planum nasale.
Histological Examination: The glabrous skin of 
planum nasale in the Eurasian lynx histologically 
consisted of the epidermis (Figure 2A) and 
dermis (Figure 2A) layers. Deep indentations 
(Dermal papillae) were seen (Figure 2B) between 
the epidermis and dermal layers. The epidermis, 
formed by the hairless keratinized squamous 
Figure 1B: An SEM image of a planum nasale’s surface, 
with the epidermal ridges (stars), shallow fissures (arrow-
head), secondary fissures (the mark), and small pores 
(stars).
Figure 1C: An SEM image of a planum nasale’s surface 
and section, with a profound groove (arrows), the epider-
mis (arrowheads), the dermis (star), and connective bun-
dles (X mark)
H. H. Ari, S. Uslu150
epithelium, was composed of the basal, spinous, 
granular, lucid, and corneum strata in the 
histological preparations stained with triple 
stain. In the samples, the basal stratum was 
formed by single layers of cells located on the 
basement membrane (arrow in Figure 2C). The 
mechanoreceptor cells were seen in the basal 
layer. These cells were thought to have endings 
in the immediate vicinity (in Figure 2C). The 
granular layer was composed of two to three cell 
rows, while the spinous layer consisted of three 
to five polyhedral cell rows (mark in Figure 2C). 
The stratum corneum was the most superficial 
on the epidermis; it is thin and has multiple 
layers of ceratinocytes. The boundaries of the 
dermis layer, which has deep and superficial 
layers, were not evident in the triple-stained 
preparations. Deep in the dermis were more 
connective fibers than in the superficial areas. 
In addition, abundant veins and venules were 
situated (star in Figure 2D–F) in the dermis 
layer. 
Figure 2: The histological view of Eurasian lynx planum nasale
Morphology and histology of the Eurasian Lynx (Lynx lynx) planum nasale 151
Scanning electron microscopy examination
The SEM surface examination showed many 
differently sized epidermal ridges in the samples 
(the stars in Figure 1B), separated from one 
another by shallow fissures (the arrowheads in 
Figure 1B). The epidermal ridges were divided 
into more small domes by secondary fissures (the 
mark in Figure 1B). The shapes of the epidermal 
ridges differ from each other, both among samples 
and between the halves of the same animal 
specimens. Small pores were situated in the 
middle of the epidermal ridges (the plus in Figure 
1B). The philtrum was a profound groove in the 
middle line of the samples (the arrows in Figure 
1B). The SEM depth module examination of the 
samples showed that both the philtrum and skin 
epidermal ridges were composed of epidermal 
layers (the arrowheads in Figure 1C) and that the 
dermal layers included dense connective bundles 
with different sizes and directions (the star and X 
mark in Figure 1C).
Discussion
The unique anatomical structures of the skin, 
such as the planum nasale, form through skin 
differentiation in various regions. The region, as 
previously described in ruminants (5, 7) and lemurs 
(3), is an extensive and easily distinguishable 
patch of moist, glabrous skin around the nostrils 
in the Eurasian lynx. In addition, the species’ 
planum nasale has a dark border on the dorsal, 
lateral, and ventral sides. 
On close macroscopic inspection, the planum 
nasale surface of the Eurasian lynx appears to be 
composed of packed polygonal plates or epidermal 
ridges, fissures, and a philtrum, as depicted in 
carnivores (8, 9), camels (5), and lemurs (3). In 
addition, the shape of the Eurasian lynx’s planum 
nasale resembles a ship anchor consisting of arm, 
palm, shank, stock, and shackle parts. The arm 
and palm are situated dorsally to the nostrils, 
while the shank and stock parts are located 
medially and ventrally, respectively, to the nostrils 
in the Euroasian lynx. As previously described 
in ruminants (5, 6, 7, 20) and lemurs (3), the 
philtrum also divides the planum nasale into two 
halves in the Eurasian lynx. Moreover, as shown 
by the gross and SEM samples, in the Eurasian 
lynx, it has been seen that the philtrum continues 
to the middle of the upper lip and divides the 
upper lip.
In the macroscopic and SEM examinations, 
we found that the shapes of the epidermal ridges 
differ between the planum nasale halves from the 
same individual and among the planum nasale of 
different individuals. The findings are similar to 
descriptions reported of primates by Clifford and 
Witmer (12) and of cattle by Solis and Maala (14). 
As described by literature (12, 14), the different 
shapes of the planum nasale’s skin plates may be 
used for individual identification of the animals 
as nose prints. In addition, we observed that the 
pores are situated on some skin plates. The skin 
plate is split into multiple secondary skin plates 
with shallow grooves. We observed that the shapes 
of the skin plates differed from of camels those 
photographed with SEM microscopy (5).
In agreement with findings from the literature 
(3, 5), we observed that the histological structure of 
the planum nasale’s skin consisted of the epidermis 
and dermal layers. However, the hypodermal 
layer could not be seen in this study. As reported 
in the literature (3, 5), a wavy border was seen 
between the epidermis and dermal layers because 
of the evident epidermis and dermal papillae in 
the histological samples. In this study, we saw 
that the basal sheet of the epidermal layer was 
formed by a single cell layer, as depicted in Lemur 
catta (3) and camels (5), whereas our findings of 
Mercel’s cells in the sheets were only similar to the 
description by Elofsson et al. (3) in Lemur catta. 
In addition, as reported by previous studies (3, 5), 
we observed that the granular sheet was thinner 
than the spinous sheet. The superficial stratum 
corneum of the planum nasale in the Eurasian 
lynx is the same as that of camels (5) and Lemur 
catta (3), in terms of thickness.
Our findings, such as dense connective fibers, 
rich blood vessels, and dermal papillae in the 
dermal layers, resemble the statements by Eshrah 
(5) in camels and Elofsson et al. (3) in Lemur catta.
Conclusion
The nasal plane or planum nasale of the 
Eurasian lynx was investigated. In this study, we 
observed that the Eurasian lynx’s planum nasale 
consists of glabrous, moist, and hairless skin 
around nostrils and that its gross morphological 
shape is in the shape of a ship anchor consisting 
H. H. Ari, S. Uslu152
of arm, palm, shank, stock, and shackle parts. 
Both the morphological and SEM investigations 
show that the planum nasale’s skin is divided by 
primary and secondary fissures and splinted into 
epidermal ridges with different sizes and shapes. 
The different surface shapes of the epidermal 
ridges in the Eurasian lynx are used for individual 
identification by nose print, as in other animals. 
In the histological examination, we saw that the 
planum nasale’s skin is composed of dermis and 
epidermal layers. The unmyelinated nerve endings 
located on the basal sheet of the epidermal layers 
may be evidence of a sensitive structure. In the 
SEM examination, we saw small pores on the 
epidermal ridges and dense bundles in the dermal 
layers. The dense bundles may create resistance 
against mechanical effects. 
Acknowledgments
We would like to thank the Republic of Turkey 
Ministry of Forestry (Sivas Branch) for permission 
to conduct studies on the Eurasian lynx (Lynx lynx).
This study was not supported by any 
foundation.
The authors declare that they have no conflict of 
interest. Statement of Animal Rights all applicable 
international, national, and/or institutional 
guidelines for the care and use of animals were 
followed.
References
1. Ozgel O, Aykut M. Macro anatomical investi-
gation on ossa membri pelvini of Anatolian bobcat 
Lynx. Pakistan J Zool 2015; 47: 1492–4.
2. Hansen K. Bobcat: master of survival. Oxford : 
University Press, 2007. 
3. Elofsson R, Tuminaite I, Kröger RHH. A com-
plex sensory organ in the nose skin of the promi-
sisian primate Lemur catta. J Morphol 2015; 276: 
649–76. doi: 10.1002/jmor.20363
4. Elofsson R, Tuminaite I, Kröger RHH. A novel 
ultrastructure on cornicocyte surface of mammalian 
nasolabial skin. J Mammal 2016; 95: 1288–94. doi: 
10.1093/jmammal/gyw112.
5. Eshrah EA. The camel rhinarium: a study re-
vealing the presence of the nasal plane in the drom-
edary camel (Camelus dromedarius) with special 
reference to its epidermal structure. Anat Histol 
Embryol 2017; 46: 65–72. doi: 10.1111/ahe.12238
6. Maya S, Chungath JJ, Ashok N, Lucy KM, 
Sreeranjini AR, Indu VR. Comparative morpho-his-
tology of muzzle in deer and goat. J Indian Vet As-
soc 2015; 12: 46–9.
7. Kalita HC, Kalita PC. Comparative gross an-
atomical studies on the muzzle of the mithun (Bos 
frontalis), yak (Bos grunniens) and zebu (Bos indi-
cus). Indian J Anim Res 2004; 38: 150–2.
8. Dyce KM, Sack WO, Wensing CJG. Textbook 
of veterinary anatomy. Saunders. 1996.
9. Getty R. Sisson and Grossman’s the anatomy 
of the domestic animals. WB Saunders. 1975.
10. König HE, Liebich HG. Veterinary anatomy 
of domestic mammals: Textbook and colour atlas. 
Schattuer. 2004.
11. Nickel R, Schummer A, Seiferle E. The vis-
cera of the domestic animals. Verlag Paul Parey. 
1973.
12. Clifford AB, Witmer LM. Case study in 
novel narial anatomy: The enigmatic nose of 
moose (Artiodactyla: Cervidae Alces alces). Jour-
nal of Zoology 2004; 262: 339–60. doi: 10.1017/
S0952836903004692
13. Kozma SM. Feasibility of animal nose print 
identification using two-dimensional image correla-
tion [Unpublished master’s dissertation]. San Diego 
University, 2004.
14. Solis JA, Maala CP. Muzzle printing as a 
method for identification of cattle and carboas. 
Philippine Journal of Medicine 1975; 14: 1–4
15. Arı HH, Kuru N, Uslu S, Özdemir Ö. Mor-
phological and histological study on the foot pads of 
the Anatolian bobcats (Lynx lynx). The Anatomical 
Record, 2018; 301: 932–8. doi: 10.1002/ar.23761
16. Anonymous. Cumhuriyet University was 
delivered dead Lynx in Sivas in order to make the 
post-mortem examination. 2016. www.sivas.or-
mansu.gov.tr/sivas/Anasayfa/resimliHaber.
17. International Committee on Veterinary 
Gross Anatomical Nomenclature. Nomina Anatom-
ica Veterinaria. 2012. 
18. Bancroft JD. Cook HC. Manual of histologi-
cal techniques. Livingstone, 1984.
19. Mahdy MAA, Abdalla KEH, Mohamed SA. 
Morphological study of the hard palate in the Egyp-
tian goat (Capra hircus): A scanning electron micro-
scopic study. Anatomia, Histologia, Embryologia, 
2018; 47: 391–397. doi: 10.1111/ahe12366 
20. Metwally MA, Huissieni HB, Kassab AA, Es-
hrah EA. Comparative anatomy of the nasal cavity 
in the buffaloes, camels and donkeys. Journal of 
Veterinary Medicine Research 2019; 9: 69–75.
Morphology and histology of the Eurasian Lynx (Lynx lynx) planum nasale 153
MORFOLOGIJA IN HISTOLOGIJA SMRČKA EVRAZIJSKEGA RISA (Lynx lynx) 
H. H. Ari, S. Uslu
Izvleček: V študiji so opisane makroskopske in mikroskopske strukture smrčka evrazijskega risa, ki je bila opravljena s 
proučevanjem tkiv treh mrtvih samic, ki so jih pridobili s pomočjo gozdarske podružnice Sivas Ministrstva za kmetijstvo in goz-
darstvo Republike Turčije. Strukturo smrčka so raziskovali z uporabo makroskopskih, histoloških metod ter uporabe vrstičnega 
elektronskega mikroskopa (SEM). Mikroskopska preiskava je pokazala, da smrček sestavlja brezdlaka, vlažna, gola koža, ki 
po obliki spominja na ladijsko sidro. Površinski del smrčka tvorijo epidermalne plošče ali grebeni, ki jih ločujejo primarne in 
sekundarne razpoke, vidne na makroskopskih slikah in s pomočjo vrstične mikroskopije. Na histoloških preparatih so bile v 
bazalni plasti smrčka epidermisa opazne Merkelove celice in živčni končiči. S pomočjo metode SEM so v plasti epidermisa 
pokazali pore, ki se nahajajo na površini epidermalnih grebenov in snope togega fibrilarnega veziva, ki segajo v plast dermisa.
Ključne besede: Evrazijski ris (Lynx rufus); morfologija; nosna ravnina; smrček