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Anatomy

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Anatomy

One of the large, detailed illustrations in Andreas Vesalius's De humani corporis fabrica, 1543, marking the rebirth of anatomy

Anatomy is the branch of biology concerned with the study of the structure of animals and their parts; it is also referred to as zootomy to separate it from human anatomy. In some of its facets, anatomy is related to embryology and comparative anatomy, which itself is closely related to evolutionary biology and phylogeny.[1] Human anatomy is one of the basic essential sciences of medicine.

The discipline of anatomy is divided into macroscopic and microscopic anatomy. Macroscopic anatomy, or gross anatomy, is the examination of an animal’s body parts using unaided eyesight. Gross anatomy also includes the branch of superficial anatomy. Microscopic anatomy involves the use of optical instruments in the study of the tissues of various structures, known as histology and also in the study of cells.

The human body. Methods have also improved dramatically, advancing from the examination of animals by dissection of carcasses and cadavers (corpses) to 20th century medical imaging techniques including X-ray, ultrasound, and magnetic resonance imaging.

Contents

  • Definition 1
  • Animal tissues 2
    • Connective tissue 2.1
    • Epithelium 2.2
    • Muscle tissue 2.3
    • Nervous tissue 2.4
  • Vertebrate anatomy 3
    • Fish anatomy 3.1
    • Amphibian anatomy 3.2
    • Reptile anatomy 3.3
    • Bird anatomy 3.4
    • Mammal anatomy 3.5
      • Human anatomy 3.5.1
  • Invertebrate anatomy 4
    • Arthropod anatomy 4.1
  • Other branches of anatomy 5
  • History 6
    • Ancient 6.1
    • Medieval to early modern 6.2
    • Late modern 6.3
  • See also 7
  • Notes 8
  • Bibliography 9
  • External links 10

Definition

Human compared to elephant frame
Anatomical chart by Vesalius, Epitome, 1543

Derived from the bile, the role of the liver in nutrition and the regulation of bodily functions.[3]

The discipline of anatomy can be subdivided into a number of branches including gross or

  • WikiProject
  • amniotic membranes which prevents them from drying out and are laid on land, or develop internally in some species. The bladder is small as nitrogenous waste is excreted as uric acid.[30]

    Anatomy of a snake. 1 esophagus, 2 trachea, 3 tracheal lungs, 4 rudimentary left lung, 5 right lung, 6 heart, 7 liver, 8 stomach, 9 air sac, 10 gallbladder, 11 pancreas, 12 spleen, 13 intestine, 14 testicles, 15 kidneys.

    Turtles are notable for their protective shells. They have an inflexible trunk encased in a horny carapace above and a plastron below. These are formed from bony plates embedded in the dermis which are overlain by horny ones and are partially fused with the ribs and spine. The neck is long and flexible and the head and the legs can be drawn back inside the shell. Turtles are vegetarians and the typical reptile teeth have been replaced by sharp, horny plates. In aquatic species, the front legs are modified into flippers.[31]

    Tuataras superficially resemble lizards but the lineages diverged in the Triassic period. There is one living species, Sphenodon punctatus. The skull has two openings (fenestrae) on either side and the jaw is rigidly attached to the skull. There is one row of teeth in the lower jaw and this fits between the two rows in the upper jaw when the animal chews. The teeth are merely projections of bony material from the jaw and eventually wear down. The brain and heart are more primitive than is the case in other reptiles and the lungs have a single chamber and lack bronchi. The tuatara has a well-developed parietal eye on its forehead.[31]

    Lizards have skulls with only one fenestra on each side, the lower bar of bone below the second fenestra having been lost. This results in the jaws being less rigidly attached which allows the mouth to open wider. Lizards are mostly quadrupeds, with the trunk held off the ground by short, sideways-facing legs, but a few species have no limbs and resemble snakes. Lizards have moveable eyelids, eardrums are present and some species have a central parietal eye.[31]

    Snakes are closely related to lizards, having branched off from a common ancestral lineage during the

    ‹The is being .› 

    External links

    • "Anatomy of the Human Body". 20th edition. 1918. Henry Gray

    Main article: Bibliography of anatomy

    Bibliography

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    2. ^ O.D.E. 2nd edition 2005
    3. ^ a b Bozman, E. F. (ed.) (1967). Everyman's Encyclopedia: Anatomy. J. M. Dent & Sons. p. 272.  
    4. ^ "Anatomy". The Free Dictionary. Farlex. 2007. Retrieved 8 July 2013. 
    5. ^ Gribble N, Reynolds K (1993). "Use of Angiography to Outline the Cardiovascular Anatomy of the Sand Crab Portunus pelagicus Linnaeus". Journal of Crustacean Biology 13 (4): 627–637. 
    6. ^ Benson KG, Forrest L (1999). "Characterization of the Renal Portal System of the Common Green Iguana (Iguana iguana) by Digital Subtraction Imaging". Journal of Zoo and Wildlife Medicine 30 (2): 235–241. 
    7. ^ "Magnetic Resonance Angiography (MRA)". Johns Hopkins Medicine. 
    8. ^ "Angiography". National Health Service. Retrieved 29 April 2014. 
    9. ^ Dorit, R. L.; Walker, W. F.; Barnes, R. D. (1991). Zoology. Saunders College Publishing. pp. 547–549.  
    10. ^ a b c Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004). Invertebrate Zoology, 7th edition. Cengage Learning. pp. 59–60.  
    11. ^ Dorland's (2012). Illustrated Medical Dictionary. Elsevier Saunders. p. 203. ISBN . 
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    13. ^ McGrath, J.A.; Eady, R.A.; Pope, F.M. (2004). Rook's Textbook of Dermatology (7th ed.). Blackwell Publishing. pp. 3.1–3.6. ISBN 978-0-632-06429-8.
    14. ^ Bernt, Karen (2010). "Glandular epithelium". Epithelial Cells. Davidson College. Retrieved 25 June 2013. 
    15. ^ Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004). Invertebrate Zoology, 7th edition. Cengage Learning. p. 103.  
    16. ^ Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004). Invertebrate Zoology, 7th edition. Cengage Learning. p. 104.  
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    27. ^ Stebbins, Robert C.; Cohen, Nathan W. (1995). A Natural History of Amphibians. Princeton University Press. pp. 24–25.  
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    29. ^ Stebbins, Robert C.; Cohen, Nathan W. (1995). A Natural History of Amphibians. Princeton University Press. pp. 26–35.  
    30. ^ Dorit, R. L.; Walker, W. F.; Barnes, R. D. (1991). Zoology. Saunders College Publishing. pp. 861–865.  
    31. ^ a b c Dorit, R. L.; Walker, W. F.; Barnes, R. D. (1991). Zoology. Saunders College Publishing. pp. 865–868.  
    32. ^ Dorit, R. L.; Walker, W. F.; Barnes, R. D. (1991). Zoology. Saunders College Publishing. p. 870.  
    33. ^ Dorit, R. L.; Walker, W. F.; Barnes, R. D. (1991). Zoology. Saunders College Publishing. p. 874.  
    34. ^ a b Dorit, R. L.; Walker, W. F.; Barnes, R. D. (1991). Zoology. Saunders College Publishing. pp. 881–895.  
    35. ^ a b Dorit, R. L.; Walker, W. F.; Barnes, R. D. (1991). Zoology. Saunders College Publishing. pp. 909–914.  
    36. ^ "Encyclopædia Britannica 2006 Ultimate Reference Suite DVD". Retrieved 15 May 2014. 
    37. ^ "Studying medicine". Medschools Online. Retrieved 27 June 2013. 
    38. ^ "Publisher's page for Gray's Anatomy. 39th edition (UK). 2004. ISBN 0-443-07168-3". Archived from the original on 12 October 2007. Retrieved 19 March 2007. 
    39. ^ "Publisher's page for Gray's Anatomy. 39th edition (US). 2004. ISBN 0-443-07168-3". Archived from the original on 9 February 2007. Retrieved 19 March 2007. 
    40. ^ a b "American Association of Anatomists". Retrieved 27 June 2013. 
    41. ^ Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004). Invertebrate Zoology, 7th edition. Cengage Learning. pp. 23–24.  
    42. ^ "Exoskeleton". Encyclopædia Britannica. Retrieved 2 July 2013. 
    43. ^ Ebling, F. J. G. "Integument". Encyclopædia Britannica. Retrieved 2 July 2013. 
    44. ^ Britannica Concise Encyclopaedia 2007
    45. ^ "O. Orkin Insect zoo". Mississippi State University. 1997. Retrieved 23 June 2013. 
    46. ^ Gullan, P.J.; Cranston, P. S. (2005). The Insects: An Outline of Entomology (3 ed.). Oxford: Blackwell Publishing. pp. 22–48.  
    47. ^ Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004). Invertebrate Zoology, 7th edition. Cengage Learning. pp. 218–225.  
    48. ^ Marieb, Elaine (2010). Human Anatomy & Physiology. San Francisco: Pearson. p. 12. 
    49. ^ Porter, R. (1997). The Greatest Benefit to Mankind: A Medical History of Humanity from Antiquity to the Present. Harper Collins. pp. 49–50.  
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    51. ^ Lang, Philippa (2013). Medicine and Society in Ptolemaic Egypt. Brill NV. p. 256. 
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    59. ^ Thorndike, Lynn (1958). A History of Magic and Experimental Science: Fourteenth and fifteenth centuries. Columbia University Press.  
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    66. ^ Rosner, Lisa. 2010. The Anatomy Murders. Being the True and Spectacular History of Edinburgh's Notorious Burke and Hare and of the Man of Science Who Abetted Them in the Commission of Their Most Heinous Crimes. University of Pennsylvania Press
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    71. ^ Waterston SW, Hutchison JD (2004). "Sir John Struthers MD FRCS Edin LLD Glasg: Anatomist, zoologist and pioneer in medical education". The Surgeon : Journal of the Royal Colleges of Surgeons of Edinburgh and Ireland 2 (6): 347–351.  
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    Notes

    See also

    [76] Short wavelength electromagnetic radiation such as

    Before the era of modern medical procedures, the main means for studying the internal structure of the body were X-ray diffraction for studying the crystal structures of proteins, nucleic acids and other biological molecules gave rise to a new field of molecular anatomy.[75]

    An electron microscope from 1973

    The teaching of anatomy in Britain was transformed by Sir John Struthers, Regius Professor of Anatomy at the University of Aberdeen from 1863 to 1889. He was responsible for setting up the system of three years of "pre-clinical" academic teaching in the sciences underlying medicine, including especially anatomy. This system lasted until the reform of medical training in 1993 and 2003. As well as teaching, he collected many vertebrate skeletons for his museum of comparative anatomy, published over 70 research papers, and became famous for his public dissection of the Tay Whale.[70][71] From 1822 the Royal College of Surgeons regulated the teaching of anatomy in medical schools.[72] Medical museums provided examples in comparative anatomy, and were often used in teaching.[73] Ignaz Semmelweis investigated puerperal fever and he discovered how it was caused. He noticed that the frequently fatal fever occurred more often in mothers examined by medical students than by midwives. The students went from the dissecting room to the hospital ward and examined women in childbirth. Semmelweis showed that when the trainees washed their hands in chlorinated lime before each clinical examination, the incidence of puerperal fever among the mothers could be reduced dramatically.[74]

    In the United States, medical schools began to be set up towards the end of the 18th century. Classes in anatomy needed a continual stream of cadavers for dissection and these were difficult to obtain. Philadelphia, Baltimore and New York were all renowned for body snatching activity as criminals raided graveyards at night, removing newly buried corpses from their coffins.[65] A similar problem existed in Britain where demand for bodies became so great that grave-raiding and even anatomy murder were practised to obtain cadavers.[66] Some graveyards were in consequence protected with watchtowers. The practice was halted in Britain by the Anatomy Act of 1832,[67][68] while in the United States, similar legislation was enacted after the physician William S. Forbes of Jefferson Medical College was found guilty in 1882 of "complicity with resurrectionists in the despoliation of graves in Lebanon Cemetery".[69]

    Late modern

    In England, anatomy was the subject of the first public lectures given in any science; these were given by the Company of Barbers and Surgeons in the 16th century, joined in 1583 by the Lumleian lectures in surgery at the Royal College of Physicians.[64]

    Andreas Vesalius (1514–1564) (Latinized from Andries van Wezel), professor of anatomy at the University of Padua, is considered the founder of modern human anatomy.[61] Originally from Brabant, Vesalius published the influential book De humani corporis fabrica ("the structure of the human body"), a large format book in seven volumes, in 1543.[62] The accurate and intricately detailed illustrations, often in allegorical poses against Italianate landscapes, are thought to have been made by the artist Jan van Calcar, a pupil of Titian.[63]

    [60][56]

    Anatomy developed little from classical times until the sixteenth century; as the historian Marie Boas writes, "Progress in anatomy before the sixteenth century is as mysteriously slow as its development after 1500 is startlingly rapid".[56]:120–121 Between 1275 and 1326, the anatomists Mondino de Luzzi, Alessandro Achillini and Antonio Benivieni at Bologna carried out the first systematic human dissections since ancient times.[57][58][59] Mondino's Anatomy of 1316 was the first textbook in the medieval rediscovery of human anatomy. It describes the body in the order followed in Mondino's dissections, starting with the abdomen, then the thorax, then the head and limbs. It was the standard anatomy textbook for the next century.[56]

    Michiel Jansz van MiereveltAnatomy lesson of Dr. Willem van der Meer, 1617
    Engraving from a picture by Tintoretto of Andreas Vesalius, about 1540
    Anatomical study of the arm, by Leonardo da Vinci, (about 1510)

    Medieval to early modern

    In the 2nd century, Galen of Pergamum, an anatomist, clinician, writer and philosopher,[53] wrote the final and highly influential anatomy treatise of ancient times.[54] He compiled existing knowledge and studied anatomy through dissection of animals.[53] He was one of the first experimental physiologists through his vivisection experiments on animals.[55] Galen's drawings, based mostly on dog anatomy, became effectively the only anatomical textbook for the next thousand years.[56] His work was known to Renaissance doctors only through Islamic Golden Age medicine until it was translated from the Greek some time in the 15th century.[56]

    The anatomy of the muscles and skeleton is described in the Hippocratic Corpus, an Ancient Greek medical work written by unknown authors.[50] Aristotle described vertebrate anatomy based on animal dissection. Praxagoras identified the difference between arteries and veins. Also in the 4th century BCE, Herophilos and Erasistratus produced more accurate anatomical descriptions based on vivisection of criminals in Alexandria during the Ptolemaic dynasty.[51][52]

    In 1600 BCE, the Edwin Smith Papyrus, an Ancient Egyptian medical text, described the heart, its vessels, liver, spleen, kidneys, hypothalamus, uterus and bladder, and showed the blood vessels diverging from the heart. The Ebers Papyrus (c. 1550 BCE) features a "treatise on the heart", with vessels carrying all the body's fluids to or from every member of the body.[49]

    Ancient

    History

    • Superficial or surface anatomy is important as the study of anatomical landmarks that can be readily seen from the exterior contours of the body.[1] It enables physicians or veterinary surgeons to gauge the position and anatomy of the associated deeper structures. Superficial is a directional term that indicates that structures are located relatively close to the surface of the body.[48]
    • Comparative anatomy relates to the comparison of anatomical structures (both gross and microscopic) in different animals.[1]
    • Artistic anatomy relates to anatomic studies for artistic reasons.

    Other branches of anatomy

    Spiders a class of arachnids have four pairs of legs; a body of two segments—a cephalothorax and an abdomen. Spiders have no wings and no antennae. They have mouthparts called chelicerae which are often connected to venom glands as most spiders are venomous. They have a second pair of appendages called pedipalps attached to the cephalothorax. These have the same segmentation as the legs and function as taste and smell organs. At the end of each pedipalp is a spoon-shaped cymbium that acts to support the pedipalp.

    thorax and an abdomen.[45] The head typically bears a pair of sensory antennae, a pair of compound eyes, one to three simple eyes (ocelli) and three sets of modified appendages that form the mouthparts. The thorax has three pairs of segmented legs, one pair each for the three segments that compose the thorax and one or two pairs of wings. The abdomen is composed of eleven segments, some of which may be fused and houses the digestive, respiratory, excretory and reproductive systems.[46] There is considerable variation between species and many adaptations to the body parts, especially wings, legs, antennae and mouthparts.[47]

    Arthropods comprise the largest phylum in the animal kingdom with over a million known invertebrate species.[44]

    Arthropod anatomy

    mesoderm is present in echinoderms, sponges and some cephalopods. Exoskeletons are derived from the epidermis and is composed of chitin in arthropods (insects, spiders, ticks, shrimps, crabs, lobsters). Calcium carbonate constitutes the shells of molluscs, brachiopods and some tube-building polychaete worms and silica forms the exoskeleton of the microscopic diatoms and radiolaria.[42] Other invertebrates may have no rigid structures but the epidermis may secrete a variety of surface coatings such as the pinacoderm of sponges, the gelatinous cuticle of cnidarians (polyps, sea anemones, jellyfish) and the collagenous cuticle of annelids. The outer epithelial layer may include cells of several types including sensory cells, gland cells and stinging cells. There may also be protrusions such as microvilli, cilia, bristles, spines and tubercles.[43]

    cilia or flagella or may proceed via the advance of pseudopodia, food may be gathered by phagocytosis, energy needs may be supplied by photosynthesis and the cell may be supported by an endoskeleton or an exoskeleton. Some protozoans can form multicellular colonies.[41]

    Daphnia a planktonic crustacean

    Invertebrate anatomy

    Academic human anatomists are usually employed by universities, medical schools or teaching hospitals. They are often involved in teaching anatomy, and research into certain systems, organs, tissues or cells.[40]

    [40]. radiology and histopathology and doctors working in some diagnostic specialties, such as surgeons A thorough working knowledge of anatomy is required by physicians, especially [39][38] The major anatomy textbook, [1] Human anatomy, physiology and biochemistry are complementary basic medical sciences, which are generally taught to medical students in their first year at medical school. Human anatomy can be taught regionally or systemically; that is, respectively, studying anatomy by bodily regions such as the head and chest, or studying by specific systems, such as the nervous or respiratory systems.

    Generally, students of certain biological sciences, paramedics, prosthetists and orthotists, physiotherapists, occupational therapists, nurses, and medical students learn gross anatomy and microscopic anatomy from anatomical models, skeletons, textbooks, diagrams, photographs, lectures and tutorials, and in addition, medical students generally also learn gross anatomy through practical experience of dissection and inspection of cadavers. The study of microscopic anatomy (or histology) can be aided by practical experience examining histological preparations (or slides) under a microscope. [37]

    Humans have the overall body plan of a mammal. Humans have a head, neck, trunk (which includes the thorax and abdomen), two arms and hands and two legs and feet.

    In the human, the development of skilled hand movements and increased brain size is likely to have evolved simultaneously.[36]
    Sagittal section of the head as seen by a MRI scan

    Human anatomy

    Mammals are amniotes, and most are viviparous, giving birth to live young. The exception to this are the egg-laying monotremes, the platypus and the echidnas of Australia. Most other mammals have a placenta through which the developing foetus obtains nourishment, but in marsupials, the foetal stage is very short and the immature young is born and finds its way to its mother's pouch where it latches on to a nipple and completes its development.[35]

    Mammals are a diverse class of animals, mostly terrestrial but some are aquatic and others have evolved flapping or gliding flight. They mostly have four limbs but some aquatic mammals have no limbs or limbs modified into fins and the forelimbs of bats are modified into wings. The legs of most mammals are situated below the trunk, which is held well clear of the ground. The bones of mammals are well ossified and their teeth, which are usually differentiated, are coated in a layer of prismatic enamel. The teeth are shed once (milk teeth) during the animal's lifetime or not at all, as is the case in cetaceans. Mammals have three bones in the middle ear and a cochlea in the inner ear. They are clothed in hair and their skin contains glands which secrete sweat. Some of these glands are specialised as mammary glands, producing milk to feed the young. Mammals breathe with lungs and have a muscular diaphragm separating the thorax from the abdomen which helps them draw air into the lungs. The mammalian heart has four chambers and oxygenated and deoxygenated blood are kept entirely separate. Nitrogenous waste is excreted primarily as urea.[35]

    Skeletons of a Great Dane and a Chihuahua

    Mammal anatomy

    The feathers are outgrowths of the epidermis and are found in localized bands from where they fan out over the skin. Large flight feathers are found on the wings and tail, contour feathers cover the bird's surface and fine down occurs on young birds and under the contour feathers of water birds. The only cutaneous gland is the single uropygial gland near the base of the tail. This produces an oily secretion that waterproofs the feathers when the bird preens. There are scales on the legs, feet and claws on the tips of the toes.[34]

    Birds are tetrapods but though their hind limbs are used for walking or hopping, their front limbs are wings covered with feathers and adapted for flight. Birds are endothermic, have a high metabolic rate, a light skeletal system and powerful muscles. The long bones are thin, hollow and very light. Air sac extensions from the lungs occupy the centre of some bones. The sternum is wide and usually has a keel and the caudal vertebrae are fused. There are no teeth and the narrow jaws are adapted into a horn-covered beak. The eyes are relatively large, particularly in nocturnal species such as owls. They face forwards in predators and sideways in ducks.[34]

    Part of a wing-drawn by Dürer
    Bird parts

    Bird anatomy

    Crocodilians are large, low-slung aquatic reptiles with long snouts and large numbers of teeth. The head and trunk are dorso-ventrally flattened and the tail is laterally compressed. It undulates from side to side to force the animal through the water when swimming. The tough keratinised scales provide body armour and some are fused to the skull. The nostrils, eyes and ears are elevated above the top of the flat head enabling them to remain above the surface of the water when the animal is floating. Valves seal the nostrils and ears when it is submerged. Unlike other reptiles, crocodilians have hearts with four chambers allowing complete separation of oxygenated and deoxygenated blood.[33]

    [32]

    Skeleton of a snake, drawn by Richard Lydekker, 1896

    Reptile anatomy

    In frogs the pelvic girdle is robust and the hind legs are much longer and stronger than the forelimbs. The feet have four or five digits and the toes are often webbed for swimming or have suction pads for climbing. Frogs have large eyes and no tail. Salamanders resemble lizards in appearance; their short legs project sideways, the belly is close to or in contact with the ground and they have a long tail. Caecilians superficially resemble earthworms and are limbless. They burrow by means of zones of muscle contractions which move along the body and they swim by undulating their body from side to side.[29]

    Amphibians are a Class (biology) of animals comprising frogs, salamanders and caecilians. They are tetrapods, but the caecilians and a few species of salamander have either no limbs or their limbs are much reduced in size. Their main bones are hollow and lightweight and are fully ossified and the vertebrae interlock with each other and have articular processes. Their ribs are usually short and may be fused to the vertebrae. Their skulls are mostly broad and short, and are often incompletely ossified. Their skin contains little keratin and lacks scales, but contains many mucous glands and in some species, poison glands. The hearts of amphibians have three chambers, two atria and one ventricle. They have a urinary bladder and nitrogenous waste products are excreted primarily as urea. Amphibians breathe by means of buccal pumping, a pump action in which air is first drawn into the buccopharyngeal region through the nostrils. These are then closed and the air is forced into the lungs by contraction of the throat.[27] They supplement this with gas exchange through the skin which needs to be kept moist.[28]

    Anatomy of frog 1 Right atrium, 2 Lungs, 3 Aorta, 4 Egg mass, 5 Colon, 6 Left atrium, 7 Ventricle, 8 Stomach, 9 Liver, 10 Gallbladder, 11 Small intestine, 12 Cloaca
    Frog skeleton
    Skeleton of Surinam horned frog
    (Ceratophrys cornuta)

    Amphibian anatomy

    The bony fish lineage shows more derived anatomical traits, often with major evolutionary changes from the features of ancient fish. They have a bony skeleton, are generally laterally flattened, have five pairs of gills protected by an operculum, and a mouth at or near the tip of the snout. The dermis is covered with overlapping scales. Bony fish have a swim bladder which helps them maintain a constant depth in the water column, but not a cloaca. They mostly spawn a large number of small eggs with little yolk which they broadcast into the water column.[26]

    Sharks and rays are basal fish with numerous primitive anatomical features similar to those of ancient fish, including skeletons composed of cartilage. Their bodies tend to be dorso-ventrally flattened, they usually have five pairs of gill slits and a large mouth set on the underside of the head. The dermis is covered with separate dermal placoid scales. They have a cloaca into which the urinary and genital passages open, but not a swim bladder. Cartilaginous fish produce a small number of large, yolky eggs. Some species are ovoviviparous and the young develop internally but others are oviparous and the larvae develop externally in egg cases.[26]

    [24] The body of a fish is divided into a head, trunk and tail, although the divisions between the three are not always externally visible. The skeleton, which forms the support structure inside the fish, is either made of cartilage, in

    Organs of a fish
    Skeleton of a butterfly fish showing the vertebral column and fin rays

    Fish anatomy

    All vertebrates have a similar basic body plan and at some point in their lives, (mostly in the embryonic stage), share the major chordate characteristics; a stiffening rod, the notochord; a dorsal hollow tube of nervous material, the neural tube; pharyngeal slits; and a tail posterior to the anus. The spinal cord is protected by the vertebral column and is above the notochord and the gastrointestinal tract is below it.[20] Nervous tissue is derived from the ectoderm, connective tissues are derived from mesoderm, and gut is derived from the endoderm. At the posterior end is a tail which continues the spinal cord and vertebrae but not the gut. The mouth is found at the anterior end of the animal, and the anus at the base of the tail.[21] The defining characteristic of a vertebrate is the vertebral column, formed in the development of the segmented series of vertebrae. In most vertebrates the notochord becomes the nucleus pulposus of the intervertebral discs. However, a few vertebrates, such as the sturgeon and the coelacanth retain the notochord into adulthood.[22] Jawed vertebrates are typified by paired appendages, fins or legs, which may be secondarily lost. The limbs of vertebrates are considered to be homologous because the same underlying skeletal structure was inherited from their last common ancestor. This is one of the arguments put forward by Charles Darwin to support his theory of evolution.[23]

    Mouse skull
    The three germ layers

    Vertebrate anatomy

    [19]

    Nervous tissue

    earthworms that can extend slowly or make rapid contractions.[15] In higher animals striated muscles occur in bundles attached to bone to provide movement and are often arranged in antagonistic sets. Smooth muscle is found in the walls of the uterus, bladder, intestines, stomach, esophagus, respiratory airways, and blood vessels. Cardiac muscle is found only in the heart, allowing it to contract and pump blood round the body.

    Cross section through skeletal muscle and a small nerve at high magnification (H&E stain)

    Muscle tissue

    Epithelial tissue is composed of closely packed cells, bound to each other by cell adhesion molecules, with little intercellular space. Epithelial cells can be squamous (flat), cuboidal or columnar and rest on a basal lamina, the upper layer of the basement membrane,[11] the lower layer is the reticular lamina lying next to the connective tissue in the extracellular matrix secreted by the epithelial cells.[12] There are many different types of epithelium, modified to suit a particular function. In the respiratory tract there is a type of ciliated epithelial lining; in the small intestine there are microvilli on the epithelial lining and in the large intestine there are intestinal villi. Skin consists of an outer layer of keratinised stratified squamous epithelium that covers the exterior of the vertebrate body. Keratinocytes make up to 95% of the cells in the skin.[13] The epithelial cells on the external surface of the body typically secrete an extracellular matrix in the form of a cuticle. In simple animals this may just be a coat of glycoproteins.[10] In more advanced animals, many glands are formed of epithelial cells.[14]

    Gastric mucosa at low magnification (H&E stain)

    Epithelium

    skeleton to support or protect the body. An exoskeleton is a thickened, rigid cuticle which is stiffened by mineralisation, as in crustaceans or by the cross-linking of its proteins as in insects. An endoskeleton is internal and present in all developed animals, as well as in many of those less developed.[10]

    Connective tissue

    Hyaline cartilage at high magnification (H&E stain)

    Animal tissues can be grouped into four basic types: connective, epithelial, muscle and nervous tissue.

    Unlike ectoderm, mesoderm and endoderm.

    The zygotes include a blastula stage in their embryonic development. Metazoans do not include the sponges, which have undifferentiated cells.[9]

    A diagram of an animal cell

    Animal tissues

    The term "anatomy" is commonly taken to refer to human anatomy. However, substantially the same structures and tissues are found throughout the rest of the animal kingdom and the term also includes the anatomy of other animals. The term zootomy is also sometimes used to specifically refer to animals. The structure and tissues of plants are of a dissimilar nature and they are studied in plant anatomy.[3]

    Anatomy can be studied using both invasive and non-invasive methods with the goal of obtaining information about the structure and organization of organs and systems.[1] Methods used include Angiography using X-rays or magnetic resonance angiography are methods to visualize blood vessels.[5][6][7][8]

    [1]

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