**4. Snake's skin and scale features**

In snakes, the skin is entirely covered with scales, specific to reptiles. The scales are set together as piles covering each other and are comprised of the upper part of mucosal layer of the skin with subcutaneous tissue below; they are keratinized and protect snakes from skin injuries and dehydration, basically to make it air-proof. When considering the position on the body, they have a different layout and shape. Scales, especially on the head, have an important role in determining the species of snakes. Smaller scales are found dorsally on the body and are placed in several rows. On the ventral, abdominal part of the body, scales are wide and transversally positioned. The shape and number of scales on the head, back, and belly are characteristic to each family, genus, and species. Scales have a nomenclature analogous to the position on the body. In "advanced" (Caenophidian) snakes, the broad belly scales and rows of dorsal scales correspond to the vertebrae, allowing scientists to count the vertebrae without dissection [14].

Scales protect the body of the snake, aid it in locomotion, allow moisture to be retained within and give simple or complex coloration patterns which help in camouflage and antipredator display. In some snakes, scales have been modified over time to serve other functions such as those of "'eyelash" fringes, and the most distinctive modification—the *rattle* of the North American rattlesnakes. The snakes also use scales for different types of movement because they have lost their limbs through the evolution process [22].

With the abdominal part of their scales, snakes can resist the unevenness of the surface and move across bare terrain such as sand and roads, where they cannot push off rocks and branches (lateral undulation type of movement) and with their muscle strength push their body forward. Besides that, it is mathematically proven that snakes also rely on the frictional properties of their scales to slide [23].

The resistance of a snake's belly scales is highest when its body is sliding sideways, rather than forward or backward. Snakes also seem to lift the parts of their bodies where friction is slowing movement the most, enabling them to slither faster. Snakes can move by folding themselves into pleats, contracting their bellies, contorting into helices or slithering in an S-shape. Scientists suggested that the snakes' belly scales, which can catch small bumps in the ground, might also aid movement. Behind the cloaca, scales are smaller and usually positioned in two lines. When closely observed, the border between the body and the tail is seen [23].

Snakes have pigmented scales; their color can change in certain species and some snakes are also albino snakes. Color of a young snake can be brighter than in adults and may also depend on the geographical position of the snake. In the cubs of green tree python (*Morelia viridis*), the color is yellowish to orange, however adult animals become green. The color of some boa species is also associated with the period of the day, where they are mostly darker at daylight and brighter at night time.

There is a polymorphism in snakes, but it is not common. It can be seen, for example, in the Turks Island Boa (*Epicrates chrysogaster*) and the Californian Royal Snake (*Lampropeltis getula californiae*), in which cells at the part of the snake may appear on individual animals forming a pattern and on the other part forming lines at the same time. During breeding of snakes, genetic mutations have emerged recently, and partial albinos are possible. During breeding, due to various mutations in the Ball Python (*Python regius*), color change may occur, and new species of morphs can be developed (**Figure 8**).

Snake skin contains pigmented cells and snakes use their color to camouflage (mimicry) or in order to give warning signs. A special form of mimicry is imitation of color, in which poor poisonous and non-lethal species of snake, such as the Arizona Mountain Kingsnake (*Lampropeltis pyromelana pyromelana*) (**Figure 9**), mimics an extremely poisonous painted coral snake (*Micrurus corallinus*) to protect themselves from predators [14].

#### **Figure 8.**

*A portrait of different patterns, colors, and morphs of Ball python (Python regius) (Photography, Leja Hrovatin, Nina Bajec, Nika Glavina, and Tilen Holynski). Very well-known and desired morphs are: Super Pastel Ivory morph (C), Piebald morph, Super Pastel Axanthic; Butter Pastel: Cinnamon, lesser (A), Super Pastel Spider, (D) Coral Glow/Banana in the comparison to normal ball python (B).*

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**Figure 9.**

*Reptilian Skin and Its Special Histological Structures DOI: http://dx.doi.org/10.5772/intechopen.84212*

Snake's skin is similarly as in lizard's consisted of germinal layer of the epidermis spinosus-like keratinocytes that alternate to hard (β) and soft (α) layers. Samples from two different species of snakes were observed histologically and skin samples were collected from different parts of the body. We have observed skin at the abdominal (ventral) part and the tail of the Burmese Python (*Python bivittatus*) (**Figure 10**) and the lip part of the Emerald Tree Boa (*Corallus caninus*) (**Figure 11**). From the outer scale surface toward the dermis are the *oberhautchen* layer, β-layer,

*Arizona Mountain Kingsnake (Lampropeltis pyromelana pyromelana) (Photography Pia Cigler).*

Iridescence is caused by the physical properties of light on the thin and transparent outer layer of the skin. When light strikes from an angle, the light spectrum is split into wavelengths of different colors. Depending on the color of the scales, this will cause iridescent effect when the snake moves. This feature is more obvious in black or dark snakes like the white-lipped python (*Liasis albertisii*) (**Figure 12**) [14]. Snakes living among the leaves are most often green, and those living in the desert are often yellowish or reddish. Snakes have no skin glands other than cloacal glands. Some species can detect infrared light. Primitive boas have pronounced sensory receptors in the skin and can detect mice at a distance of 15 cm. Between the nostrils and the eye, in some snakes, there are special infrared receptors (pits) that allow them to feel hot-blooded animals and to attack them in the dark. These receptors are innerved with *n. mandibularis*, *n. maxillaris,* and *n. ophthalmicus* (branch of *n. trigeminus*). Along the upper and lower lumbar scales, there are fewer pits, which are also innervated by the branches of *n. trigeminus*. These organs are

At the ends of the tails of rattlesnakes (*Crotalus sp.*), there is a special anatomical adjustment—a rattle. Also, their name derives from the Greek word *krótalοn*, which means "rattle" or "castanet," and refers to the rattle on the end of the tail which makes this group (genera *Crotalus* and *Sistrurus*) very distinctive [26]. The rattle consists of up to 20 loosely interlocking hollow shells, each of which is at one point the scale covering the tip of the tail. Their number depends on the type and gender of the animal. In most other snakes, the tail tip is cone-shaped and not much thicker than the rest of the skin. It is shed along with the rest of molt. However, in rattlesnakes, it does not shed, and it also gets elongated, since younger specimens may shed three to four times per year, every time adding a new segment to the rattle. The end of the tail is much thicker and round shaped at the end, with one or two annular constrictions to prevent it from falling off. Before each shedding, a new button will

mesos layer, α-layer, lacunar layer, and the clear layer [1, 24, 25].

extremely sensitive to temperature changes of as much as 0.002°C [14].

*Reptilian Skin and Its Special Histological Structures DOI: http://dx.doi.org/10.5772/intechopen.84212*

*Veterinary Anatomy and Physiology*

morphs can be developed (**Figure 8**).

themselves from predators [14].

contorting into helices or slithering in an S-shape. Scientists suggested that the snakes' belly scales, which can catch small bumps in the ground, might also aid movement. Behind the cloaca, scales are smaller and usually positioned in two lines. When closely observed, the border between the body and the tail is seen [23].

Snakes have pigmented scales; their color can change in certain species and some snakes are also albino snakes. Color of a young snake can be brighter than in adults and may also depend on the geographical position of the snake. In the cubs of green tree python (*Morelia viridis*), the color is yellowish to orange, however adult animals become green. The color of some boa species is also associated with the period of the day, where they are mostly darker at daylight and brighter at night time. There is a polymorphism in snakes, but it is not common. It can be seen, for example, in the Turks Island Boa (*Epicrates chrysogaster*) and the Californian Royal Snake (*Lampropeltis getula californiae*), in which cells at the part of the snake may appear on individual animals forming a pattern and on the other part forming lines at the same time. During breeding of snakes, genetic mutations have emerged recently, and partial albinos are possible. During breeding, due to various mutations in the Ball Python (*Python regius*), color change may occur, and new species of

Snake skin contains pigmented cells and snakes use their color to camouflage (mimicry) or in order to give warning signs. A special form of mimicry is imitation of color, in which poor poisonous and non-lethal species of snake, such as the Arizona Mountain Kingsnake (*Lampropeltis pyromelana pyromelana*) (**Figure 9**), mimics an extremely poisonous painted coral snake (*Micrurus corallinus*) to protect

**144**

**Figure 8.**

*A portrait of different patterns, colors, and morphs of Ball python (Python regius) (Photography, Leja Hrovatin, Nina Bajec, Nika Glavina, and Tilen Holynski). Very well-known and desired morphs are: Super Pastel Ivory morph (C), Piebald morph, Super Pastel Axanthic; Butter Pastel: Cinnamon, lesser (A), Super* 

*Pastel Spider, (D) Coral Glow/Banana in the comparison to normal ball python (B).*

**Figure 9.** *Arizona Mountain Kingsnake (Lampropeltis pyromelana pyromelana) (Photography Pia Cigler).*

Snake's skin is similarly as in lizard's consisted of germinal layer of the epidermis spinosus-like keratinocytes that alternate to hard (β) and soft (α) layers. Samples from two different species of snakes were observed histologically and skin samples were collected from different parts of the body. We have observed skin at the abdominal (ventral) part and the tail of the Burmese Python (*Python bivittatus*) (**Figure 10**) and the lip part of the Emerald Tree Boa (*Corallus caninus*) (**Figure 11**). From the outer scale surface toward the dermis are the *oberhautchen* layer, β-layer, mesos layer, α-layer, lacunar layer, and the clear layer [1, 24, 25].

Iridescence is caused by the physical properties of light on the thin and transparent outer layer of the skin. When light strikes from an angle, the light spectrum is split into wavelengths of different colors. Depending on the color of the scales, this will cause iridescent effect when the snake moves. This feature is more obvious in black or dark snakes like the white-lipped python (*Liasis albertisii*) (**Figure 12**) [14].

Snakes living among the leaves are most often green, and those living in the desert are often yellowish or reddish. Snakes have no skin glands other than cloacal glands. Some species can detect infrared light. Primitive boas have pronounced sensory receptors in the skin and can detect mice at a distance of 15 cm. Between the nostrils and the eye, in some snakes, there are special infrared receptors (pits) that allow them to feel hot-blooded animals and to attack them in the dark. These receptors are innerved with *n. mandibularis*, *n. maxillaris,* and *n. ophthalmicus* (branch of *n. trigeminus*). Along the upper and lower lumbar scales, there are fewer pits, which are also innervated by the branches of *n. trigeminus*. These organs are extremely sensitive to temperature changes of as much as 0.002°C [14].

At the ends of the tails of rattlesnakes (*Crotalus sp.*), there is a special anatomical adjustment—a rattle. Also, their name derives from the Greek word *krótalοn*, which means "rattle" or "castanet," and refers to the rattle on the end of the tail which makes this group (genera *Crotalus* and *Sistrurus*) very distinctive [26]. The rattle consists of up to 20 loosely interlocking hollow shells, each of which is at one point the scale covering the tip of the tail. Their number depends on the type and gender of the animal. In most other snakes, the tail tip is cone-shaped and not much thicker than the rest of the skin. It is shed along with the rest of molt. However, in rattlesnakes, it does not shed, and it also gets elongated, since younger specimens may shed three to four times per year, every time adding a new segment to the rattle. The end of the tail is much thicker and round shaped at the end, with one or two annular constrictions to prevent it from falling off. Before each shedding, a new button will

#### **Figure 10.**

*Skin histology of the tail (A, B) and ventral part (B, D) of Burmese Python (Python bivittatus). Skin from the tail and ventral part of the Burmese Python was stained with H&E staining. The sample was taken in the resting stage of the epidermis, when the animal was not in the process of ecdysis. In epidermis, the most visible part is the basal layer with keratinocytes with nuclei, which are dividing with mitosis. In figure (A) and (B), the existence of the overlapping scales and hinge region is observed. The melanin pigment is not evenly spread on all surfaces of scales. Mostly, it is observed in the overlapping scale and much less from the hinge region to the scale, which is overlapped. Approximately five layers were identified by microscopic observation. These were the oberhautchen, β-layer, the mesos layer, α-layer, and dermis. The β- and α-layers consisted of cells which become keratinized with the production of two types of keratin (β- and α-keratins). The oberhautchen did not show smooth characteristics, followed the inner scale surface and hinge region composed of thin β-layer. At the abdominal part of the skin, the epidermis is thicker. Dermis contains many more melanophores. In the dermis, fibrous connective tissue, vessels, nerves, melanophores, and Merkel mechanoreceptor cells are observed. In dermis connective tissue together with collagen fibers hard interesting pattern, which was distinctive in both samples. (A) 100× magnification, (B) 400× magnification.*

develop inside the last one and before the skin is shed, the tip of new button shrinks. This process continues, and an appendage consists of a number of interlocking segments that sound characteristically. The sound is generated by friction one button to another, especially when snake feels endangered. In grass snakes (*Natrix natrix*)*,* pine snakes (*Pituophis spp.*)*,* and kingsnakes (*Lampropeltis spp*.), similar sounds are produced as heard in rattlesnakes by shaking their tail or other body parts against the surface where they are [27].

Snakes periodically molt their scaly skins and acquire new ones. This permits replacement of old worn out skin, disposal of parasites, and is thought to allow the snake to grow. The shape and arrangement of scales are used to identify snake species [14].

**147**

surfaces [28].

**Figure 11.**

**Figure 12.**

*400× magnification.*

*Reptilian Skin and Its Special Histological Structures DOI: http://dx.doi.org/10.5772/intechopen.84212*

**5. Skin and scute features in crocodiles**

be the primitive form of dermal armor in reptiles [8].

*Iridescence in white-lipped python (Liasis albertisii) (Photography Valentina Kubale).*

In crocodiles and turtles, the dermal armor is formed from the deeper dermis rather than the epidermis and does not form the same sort of overlapping structure as snake scales. These dermal scales are more properly called scutes. Similar dermal scutes are found in the feet of birds and tails of some mammals and are believed to

*Skin histology of the lip of the Emerald Tree Boa (Corallus caninus). Skin from the lip of the Emerald Tree Boa was stained with H&E staining. The sample was taken in the resting stage of the epidermis, when the animal was not in the process of ecdysis. In epidermis (B), the most visible part is the basal layer with keratinocytes containing nuclei, which are dividing under mitosis. Very visible is also the melanophore layer. This side is oriented toward the lip side. Keratinized epithelium (at the bottom of panel (A)) is more heavily keratinized and fewer melanophores are observed. (A, C) 100× magnification, (C, D)* 

The crocodile skin has horny plates, named scutes, in which shape, number, and position are important for the identification of the species. They can also become similar to bones and form an outer bone armor. The horny plates on the back are referred as the back shield, and below are dermal plates (4–10 longitudinal plates whose number varies depending on the animal species). On the abdominal side beneath the horny scutes, there are no bone plates. On the tail, scutes form rings with two rows continuing in one row of scutes by the end of the tail. The position of the horny scutes on the head is characteristic for each animal species. On the head beneath the horny scutes, bone plates are located. Unlike other reptiles, crocodiles do not shed their scutes, and they are renewed by scrubbing against different outer

*Reptilian Skin and Its Special Histological Structures DOI: http://dx.doi.org/10.5772/intechopen.84212*

#### **Figure 11.**

*Veterinary Anatomy and Physiology*

**146**

species [14].

**Figure 10.**

the surface where they are [27].

*samples. (A) 100× magnification, (B) 400× magnification.*

develop inside the last one and before the skin is shed, the tip of new button shrinks. This process continues, and an appendage consists of a number of interlocking segments that sound characteristically. The sound is generated by friction one button to another, especially when snake feels endangered. In grass snakes (*Natrix natrix*)*,* pine snakes (*Pituophis spp.*)*,* and kingsnakes (*Lampropeltis spp*.), similar sounds are produced as heard in rattlesnakes by shaking their tail or other body parts against

*Skin histology of the tail (A, B) and ventral part (B, D) of Burmese Python (Python bivittatus). Skin from the tail and ventral part of the Burmese Python was stained with H&E staining. The sample was taken in the resting stage of the epidermis, when the animal was not in the process of ecdysis. In epidermis, the most visible part is the basal layer with keratinocytes with nuclei, which are dividing with mitosis. In figure (A) and (B), the existence of the overlapping scales and hinge region is observed. The melanin pigment is not evenly spread on all surfaces of scales. Mostly, it is observed in the overlapping scale and much less from the hinge region to the scale, which is overlapped. Approximately five layers were identified by microscopic observation. These were the oberhautchen, β-layer, the mesos layer, α-layer, and dermis. The β- and α-layers consisted of cells which become keratinized with the production of two types of keratin (β- and α-keratins). The oberhautchen did not show smooth characteristics, followed the inner scale surface and hinge region composed of thin β-layer. At the abdominal part of the skin, the epidermis is thicker. Dermis contains many more melanophores. In the dermis, fibrous connective tissue, vessels, nerves, melanophores, and Merkel mechanoreceptor cells are observed. In dermis connective tissue together with collagen fibers hard interesting pattern, which was distinctive in both* 

Snakes periodically molt their scaly skins and acquire new ones. This permits replacement of old worn out skin, disposal of parasites, and is thought to allow the snake to grow. The shape and arrangement of scales are used to identify snake *Skin histology of the lip of the Emerald Tree Boa (Corallus caninus). Skin from the lip of the Emerald Tree Boa was stained with H&E staining. The sample was taken in the resting stage of the epidermis, when the animal was not in the process of ecdysis. In epidermis (B), the most visible part is the basal layer with keratinocytes containing nuclei, which are dividing under mitosis. Very visible is also the melanophore layer. This side is oriented toward the lip side. Keratinized epithelium (at the bottom of panel (A)) is more heavily keratinized and fewer melanophores are observed. (A, C) 100× magnification, (C, D) 400× magnification.*

**Figure 12.** *Iridescence in white-lipped python (Liasis albertisii) (Photography Valentina Kubale).*
