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Anatomy and physiology

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Abstract

There are over 9000 species of extant reptiles, each of which has evolved in response to the unique environmental pressures of its native habitat. However, a number of anatomical and physiological features are common throughout the taxon, and a sound understanding of these basic principles is essential for the successful management of pathological conditions in herpetofauna.

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Figures

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1.1 Reptiles such as this lace monitor are ectothermic animals and regulate their body temperature by moving between areas of hot and cold.
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1.2 Behavioural thermoregulation allows reptiles to elevate their body temperature above ambient temperature.
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1.4 Some species of reptiles can enhance their ability to absorb thermal radiation by altering their posture or body position relative to the sun. This inland bearded dragon is increasing its surface area by flattening out.
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1.5 Osteoderms are a prominent feature of reptilian skin. Note the presence of large calcified scales in this radiograph of a shingleback lizard.
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1.6 (a) Dorsal and (b) ventral views of the osteoderms of the shell of a semiaquatic chelonian; the common long-necked turtle.
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1.7 (a) Dorsal and (b) ventral views of the scutes of the chelonian shell.
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1.8 Femoral pores are prominent in some male lizards when they reach sexual maturity as is the case with this inland bearded dragon.
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1.9 In this common long-necked turtle, the Rathke’s gland is arrowed and is used by some chelonians as a deterrent against predation.
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1.10 (a) Labial pits (arrowed) in a coastal carpet python and (b) pit organ (arrowed) in a Wagler’s pit viper.
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1.11 Shingleback lizard parietal eye (arrowed).
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1.12 Chameleons are able to change colour rapidly and spectacularly. The primary function of their colour change is communication.
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1.13 Some lizards, such as this spiny-tailed monitor, shed in patches and the entire skin is shed over a period of weeks.
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1.14 The skulls of chelonians are classified as anapsid (no temporal fossa).
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1.15 The skulls of squamates such as (a) the eastern tiger snake and (b) the inland bearded dragon are diapsid (two temporal fossae).
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1.16 Varanids have pleurodont dentition. The teeth are attached to the medial aspect of the jaw.
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1.17 Ribs are attached to every trunk vertebra in all species of reptiles.
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1.18 The limbs of reptiles show variation depending on ecology: (a) terrestrial – shingleback lizard; (b) arboreal – lace monitor; (c) semiaquatic – Macquarie river turtle; (d) marine – green sea turtle.
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1.19 In members of the Boidae and Pythonidae, a vestigial pelvic girdle exists in the form of femoral spurs. Cranial is to the right of the picture.
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1.20 The chelonian heart, as shown in this common long-necked turtle, lies deep to the margins of the humeral and pectoral scutes.
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1.21 As shown in this eastern blue-tongue lizard, the heart of lizards is commonly located within the pectoral girdle.
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1.22 In some lizards, such as varanids, the heart lies caudally within the coelom as demonstrated in this lace monitor.
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1.23 In most snakes, for example in this eastern tiger snake, the heart is found at 22–33% of the snout–vent length.
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1.24 The positions of the internal organs of snakes relative to body length; family mean data. S–C = snout to cloaca length. (Courtesy of Helen McCracken)
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1.25 Chelonian heart. (a) Dorsal view. (b) Ventral view. (Courtesy of Jeanette Wyneken and reproduced from with permission from Elsevier)
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1.26 Lizard heart. (a) Dorsal view. (b) Ventral view. (Courtesy of Jeanette Wyneken and reproduced from with permission from Elsevier)
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1.27 Snake heart. (a) Dorsal view. (b) Ventral view. (Courtesy of Jeanette Wyneken and reproduced from with permission from Elsevier)
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1.28 Pattern of blood flow through the heart of a non-crocodilian reptile.
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1.29 Pattern of blood flow through the heart of a non-crocodilian reptile with a right-to-left shunt.
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1.30 The air exchange surfaces of reptiles are known as ediculae and faveolae and they have a honeycomb-like appearance as seen in this Stimson’s python.
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1.31 (a) The chelonian glottis is located at the base of the fleshy tongue. (b) The position of the lizard glottis varies depending on species and can be situated rostrally, as in this monitor, or more caudally. (c) The snake glottis is located rostrally near the base of the tongue.
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1.32 The trachea of chelonians is short and usually bifurcates in the cervical region. Cranial is to the right of the picture.
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1.33 The lungs of chelonians are located in the dorsal coelomic space as indicated by these (a) craniocaudal and (b) lateral whole-body radiographs. Cranial is to the left of the picture.
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1.34 The lungs of chelonians are of equal size and extend to the cranial poles of the kidneys, as exposed in this common long-necked turtle. Note: the kidneys are obscured by the lungs.
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1.35 The lungs of lizards are of comparable size and occupy the cranial portion of the coelomic cavity. The liver has been retracted in this picture of an eastern blue-tongue lizard, to expose the lungs. Cranial is to the top of the picture.
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1.36 Most snakes have a single lung with the left side being vestigial or absent altogether, as seen in this lowland copperhead. The functional lung transitions into a non-respiratory air sac caudally. Cranial is to the left of the picture.
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1.37 More primitive species of snakes such as boas and pythons have left and right lungs as seen in this olive python. Cranial is to the left of the picture.
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1.38 Chameleons, as demonstrated by this Oustalet’s chameleon, have a large prehensile tongue that they use to capture prey many body lengths away.
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1.39 (a) Snakes (e.g. the Madagascar ground boa) and (b) varanid lizards (e.g. the lace monitor) have a thin forked mobile tongue that plays no role in prehension of food.
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1.40 The fangs of venomous snakes, such as this lowland copperhead, are supplied by the venom gland.
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1.41 The Gila monster is a lizard that has evolved a venomous bite to aid in defence. (Courtesy of Damian Goodall)
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1.42 Prominent folds in the gastric mucosa of snakes allow for marked expansion of the stomach for digestion of large prey items. Cranial is to the left of the picture.
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1.43 Oxyurid nematodes are common in the caecum and colon of reptiles, and they are thought to aid in the mechanical breakdown of intestinal contents.
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1.44 In snakes, the gall bladder lies caudal to the liver and is associated with the pancreas and spleen. Cranial is to the left of the picture.
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1.45 Some reptiles kill their prey by crushing it with powerful jaws, which is the technique demonstrated here by the panther chameleon.
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1.46 Venomous snakes, such as this western diamondback rattlesnake, incapacitate prey items by delivering venom through a bite. © Shutterstock
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1.48 In chelonians, the kidneys are located near the pelvic canal, adhered to the dorsocaudal carapace. Cranial is to the top of the picture.
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1.49 Eastern blue-tongue lizard: in most lizards the kidneys are located deep within the pelvic canal and in some species extend into the tail base. Cranial is to the top of the picture.
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1.50 The kidneys of varanids (arrowed) are found in the caudal coelom as seen in the lace monitor.
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1.51 The kidneys of snakes are located in the caudal coelomic cavity with the right kidney situated cranially to the left kidney.
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1.52 Renal and vascular anatomy of the generic chelonian. (Courtesy of Jeanette Wyneken and reproduced from with permission from Elsevier)
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1.53 Renal and vascular anatomy of the generic lizard. (Courtesy of Jeanette Wyneken and reproduced from with permission from Elsevier)
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1.54 Renal and vascular anatomy of the generic snake. (Courtesy of Jeanette Wyneken and reproduced from with permission from Elsevier)
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1.55 All chelonians, including this common long-necked turtle, possess a urinary bladder (arrowed).
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1.56 A urinary bladder (arrowed) is only present in some species of lizards, such as this eastern blue-tongue lizard. Cranial is to the top of the picture.
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1.57 Common long-necked turtle: the reproductive tract of the male chelonian in relationship to other organs. L = ligament; LL = left liver lobe; LU = lung; RL = right liver lobe; T = testis.
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1.58 Snakes and lizards (e.g. lace monitor pictured) have paired hemipenes located within the tail base that evert for copulation.
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1.59 In some species of lizard, such as varanids (e.g. lace monitor pictured), the hemipenes are characterized by the presence of ossified hemibacula (arrowed).
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1.60 An eastern blue-tongue lizard showing the female reproductive tract which consists of paired ovaries similarly located to the testes. CO = colon; LL = left liver lobe; OF = ovarian follicle; RL = right liver lobe; UB = urinary bladder.
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1.61 The common long-necked turtle, chelonian female reproductive system dissected from the body. CO = colon; OD = oviduct; OV = ovary; UB = urinary bladder. Cranial is to the left of picture.
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1.62 The eggs of reptiles show varying degrees of calcification. Chelonian eggs such as these are typically more rubbery.
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1.63 The brain of reptiles can be divided into various segments that can be distinguished both by gross morphology and microscopically.

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