Skeleton

The skeleton is the body part that forms the supporting structure of an organism. It can also be seen as the bony frame work of the body which provides support, shape and protection to the soft tissues and delicate organs in animals. There are several different skeletal types: the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside the body, the hydroskeleton, and the cytoskeleton. The term comes from Greek σκελετός (skeletós), meaning 'dried up'.[1]

Skeleton
Horse and Man
A horse and human skeleton placed in a display in the Australian Museum, Sydney.
Vein skeleton of a leaf (de-ghosted)
Vein skeleton of a leaf. Veins contain lignin that make them harder to degrade for microorganisms. The leaf came from Magnolia doltsopa(Magnoliaceae).
Details
Identifiers
Greekσκελετός
MeSHD012863
Anatomical terminology

Types of skeletons

There are two major types of skeletons: solid and fluid. Solid skeletons can be internal, called an endoskeleton, or external, called an exoskeleton, and may be further classified as pliant (elastic/movable) or rigid (hard/non-movable).[2] Fluid skeletons are always internal.

Exoskeleton

Exoskeletons are external, and are found in many invertebrates; they enclose and protect the soft tissues and organs of the body. Some kinds of exoskeletons undergo periodic moulting or edolysis as the animal grows, as is the case in many arthropods including insects and crustaceans.

The exoskeleton of insects is not only a form of protection, but also serves as a surface for muscle attachment, as a watertight protection against drying, and as a sense organ to interact with the environment. The shell of mollusks also performs all of the same functions, except that in most cases it does not contain sense organs.

An external skeleton can be quite heavy in relation to the overall mass of an animal, so on land, organisms that have an exoskeleton are mostly relatively small. Somewhat larger aquatic animals can support an exoskeleton because weight is less of a consideration underwater. The southern giant clam, a species of extremely large saltwater clam in the Pacific Ocean, has a shell that is massive in both size and weight. Syrinx aruanus is a species of sea snail with a very large shell.

Endoskeleton

Beaver skeleton
A beaver skeleton on display at The Museum of Osteology, Oklahoma City, Oklahoma.

The endoskeleton is the internal support structure of an animal, composed of mineralized tissue and is typical of vertebrates. Endoskeletons vary in complexity from functioning purely for support (as in the case of sponges), to serving as an attachment site for muscles and a mechanism for transmitting muscular forces. A true endoskeleton is derived from mesodermal tissue. Such a skeleton is present in echinoderms and chordates.

Pliant skeletons

Pliant skeletons are capable of movement; thus, when stress is applied to the skeletal structure, it deforms and then reverts to its original shape. This skeletal structure is used in some invertebrates, for instance in the hinge of bivalve shells or the mesoglea of cnidarians such as jellyfish. Pliant skeletons are beneficial because only muscle contractions are needed to bend the skeleton; upon muscle relaxation, the skeleton will return to its original shape. Cartilage is one material that a pliant skeleton may be composed of, but most pliant skeletons are formed from a mixture of proteins, polysaccharides, and water.[2] For additional structure or protection, pliant skeletons may be supported by rigid skeletons. Organisms that have pliant skeletons typically live in water, which supports body structure in the absence of a rigid skeleton.[3]

Rigid skeletons

Rigid skeletons are not capable of movement when stressed, creating a strong support system most common in terrestrial animals. Such a skeleton type used by animals that live in water are more for protection (such as barnacle and snail shells) or for fast-moving animals that require additional support of musculature needed for swimming through water. Rigid skeletons are formed from materials including chitin (in arthropods), calcium compounds such as calcium carbonate (in stony corals and mollusks) and silicate (for diatoms and radiolarians).

Cytoskeleton

The cytoskeleton (gr. kytos = cell) is used to stabilize and preserve the form of the cells. It is a dynamic structure that maintains cell shape, protects the cell, enables cellular motion (using structures such as flagella, cilia and lamellipodia), and plays important roles in both intracellular transport (the movement of vesicles and organelles, for example) and cellular division.

Fluid skeletons

Hydrostatic skeleton (hydroskeleton)

A hydrostatic skeleton is a semi-rigid, soft tissue structure filled with liquid under pressure, surrounded by muscles. Longitudinal and circular muscles around their body sectors allow movement by alternate lengthening and contractions along their lengths. A common example of this is the earthworm.

Organisms with skeletons

Invertebrates

The endoskeletons of echinoderms and some other soft-bodied invertebrates such as jellyfish and earthworms are also termed hydrostatic; a body cavity the coelom is filled with coelomic fluid and the pressure from this fluid acts together with the surrounding muscles to change the organism's shape and produce movement.

Sponges

The skeleton of sponges consists of microscopic calcareous or silicious spicules. The demosponges include 90% of all species of sponges. Their "skeletons" are made of spicules consisting of fibers of the protein spongin, the mineral silica, or both. Where spicules of silica are present, they have a different shape from those in the otherwise similar glass sponges.[4]

Echinoderms

The skeleton of the echinoderms, which include, among other things, the starfish, is composed of calcite and a small amount of magnesium oxide. It lies below the epidermis in the mesoderm and is within cell clusters of frame-forming cells. This structure formed is porous and therefore firm and at the same time light. It coalesces into small calcareous ossicles (bony plates), which can grow in all directions and thus can replace the loss of a body part. Connected by joints, the individual skeletal parts can be moved by the muscles.

Vertebrates

Huxley - Mans Place in Nature
Pithecometra: From Thomas Huxley's 1863 Evidence as to Man's Place in Nature, the compared skeletons of apes to humans.

In most vertebrates, the main skeletal component is referred to as bone. These bones compose a unique skeletal system for each type of animal. Another important component is cartilage which in mammals is found mainly in the joint areas. In other animals, such as the cartilaginous fishes, which include the sharks, the skeleton is composed entirely of cartilage. The segmental pattern of the skeleton is present in all vertebrates (mammals, birds, fish, reptiles and amphibians) with basic units being repeated. This segmental pattern is particularly evident in the vertebral column and the ribcage.

Bones in addition to supporting the body also serve, at the cellular level, as calcium and phosphate storage.

Fish

The skeleton, which forms the support structure inside the fish is either made of cartilage as in the (Chondrichthyes), or bones as in the (Osteichthyes). The main skeletal element is the vertebral column, composed of articulating vertebrae which are lightweight yet strong. The ribs attach to the spine and there are no limbs or limb girdles. They are supported only by the muscles. The main external features of the fish, the fins, are composed of either bony or soft spines called rays, which with the exception of the caudal fin (tail fin), have no direct connection with the spine. They are supported by the muscles which compose the main part of the trunk.

Birds

The bird skeleton is highly adapted for flight. It is extremely lightweight, yet still strong enough to withstand the stresses of taking off, flying, and landing. One key adaptation is the fusing of bones into single ossifications, such as the pygostyle. Because of this, birds usually have a smaller number of bones than other terrestrial vertebrates. Birds also lack teeth or even a true jaw, instead having evolved a beak, which is far more lightweight. The beaks of many baby birds have a projection called an egg tooth, which facilitates their exit from the amniotic egg.

Marine mammals

To facilitate the movement of marine mammals in water, the hind legs were either lost altogether, as in the whales and manatees, or united in a single tail fin as in the pinnipeds (seals). In the whale, the cervical vertebrae are typically fused, an adaptation trading flexibility for stability during swimming.[5][6]

Humans

Leonardo Skeleton 1511
Study of Skeletons, c. 1510, by Leonardo da Vinci

The human skeleton consists of both fused and individual bones supported and supplemented by ligaments, tendons, muscles and cartilage. It serves as a scaffold which supports organs, anchors muscles, and protects organs such as the brain, lungs, heart and spinal cord. Although the teeth do not consist of tissue commonly found in bones, the teeth are usually considered as members of the skeletal system.[7] The biggest bone in the body is the femur in the upper leg, and the smallest is the stapes bone in the middle ear. In an adult, the skeleton comprises around 14% of the total body weight,[8] and half of this weight is water.

Fused bones include those of the pelvis and the cranium. Not all bones are interconnected directly: There are three bones in each middle ear called the ossicles that articulate only with each other. The hyoid bone, which is located in the neck and serves as the point of attachment for the tongue, does not articulate with any other bones in the body, being supported by muscles and ligaments.

There are 206 bones in the adult human skeleton, although this number depends on whether the pelvic bones (the hip bones on each side) are counted as one or three bones on each side (ilium, ischium, and pubis), whether the coccyx or tail bone is counted as one or four separate bones, and does not count the variable wormian bones between skull sutures. Similarly, the sacrum is usually counted as a single bone, rather than five fused vertebrae. There is also a variable number of small sesamoid bones, commonly found in tendons. The patella or kneecap on each side is an example of a larger sesamoid bone. The patellae are counted in the total, as they are constant. The number of bones varies between individuals and with age – newborn babies have over 270 bones[9][10][11] some of which fuse together. These bones are organized into a longitudinal axis, the axial skeleton, to which the appendicular skeleton is attached.[12]

The human skeleton takes 20 years before it is fully developed. In many animals, the skeleton bones contain marrow, which produces blood cells.

There exist several general differences between the male and female skeletons. The male skeleton, for example, is generally larger and heavier than the female skeleton. In the female skeleton, the bones of the skull are generally less angular. The female skeleton also has wider and shorter breastbone and slimmer wrists. There exist significant differences between the male and female pelvis which are related to the female's pregnancy and childbirth capabilities. The female pelvis is wider and shallower than the male pelvis. Female pelvises also have an enlarged pelvic outlet and a wider and more circular pelvic inlet. The angle between the pubic bones is known to be sharper in males, which results in a more circular, narrower, and near heart-shaped pelvis.[13][14]

Bones and cartilage

Bone

Bones are rigid organs that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue. Bones have a variety of shapes with a complex internal and external structure they are also lightweight, yet strong and hard. One of the types of tissue that makes up bone tissue is mineralized tissue and this gives it rigidity and a honeycomb-like three-dimensional internal structure. Other types of tissue found in bones include marrow, endosteum and periosteum, nerves, blood vessels and cartilage. There are 206 bones in the adult human body[15] and 270 in an infant.[16]

Cartilage

During embryogenesis the precursor to bone development is cartilage. Much of this substance is then replaced by bone during the second and third trimester, after the flesh such as muscle has formed around it; forming the skeleton. Cartilage is a stiff and inflexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs. It is not as hard and rigid as bone but is stiffer and less flexible than muscle.

Cartilage is composed of specialized cells called chondrocytes that produce a large amount of extracellular matrix composed of Type II collagen (except Fibrocartilage which also contains type I collagen) fibers, abundant ground substance rich in proteoglycan, and elastin fibers. Cartilage is classified in three types, elastic cartilage, hyaline cartilage and fibrocartilage, which differ in the relative amounts of these three main components.

Unlike other connective tissues, cartilage does not contain blood vessels. The chondrocytes are supplied by diffusion, helped by the pumping action generated by compression of the articular cartilage or flexion of the elastic cartilage. Thus, compared to other connective tissues, cartilage grows and repairs more slowly.

In popular culture

In Western culture, the skeleton is oftentimes seen as a fearful symbol of death and the paranormal. It is a popular motif in the holiday Halloween, as well as Day of the Dead.

See also

References

  1. ^ Oxford Dictionary of English 2nd edition 2005
  2. ^ a b Barnes, Edward E.; Fox, Richard S.; Barnes, Robert D. (2003). Invertebrate zoology : a functional evolutionary approach (7. ed.). Belmont, Calif. [u.a.]: Thomson, Brooks/Cole. ISBN 0-03-025982-7.
  3. ^ Pechenik, Jan A. (2015). Biology of the Invertebrates (Seventh ed.). New York: McGraw-Hill Education. ISBN 978-0-07-352418-4.
  4. ^ Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia: Holt-Saunders International. pp. 105–106. ISBN 0-03-056747-5.
  5. ^ "Beluga Whale". Yellowmagpie.com. 27 June 2012. Archived from the original on 21 May 2013. Retrieved 12 August 2013.
  6. ^ "About Whales". Whalesalive.org.au. 26 June 2009. Archived from the original on 12 August 2013. Retrieved 12 August 2013.
  7. ^ "Skeletal System: Facts, Function & Diseases". Live Science. Archived from the original on 7 March 2017. Retrieved 7 March 2017.
  8. ^ William W. Reynolds & William J. Karlotski (1977). "The Allometric Relationship of Skeleton Weight to Body Weight in Teleost Fishes: A Preliminary Comparison with Birds and Mammals". Copeia: 160–163. doi:10.2307/1443520.
  9. ^ Miller, Larry (9 December 2007). "We're Born With 270 Bones. As Adults We Have 206". Ground Report. Archived from the original on 14 August 2016.
  10. ^ "How many bones does the human body contain?". Yahoo!. 8 August 2001. Archived from the original on 11 July 2011. Retrieved 4 March 2010.
  11. ^ http://education.sdsc.edu/download/enrich/exploring_human.pdf
  12. ^ Tözeren, Aydın (2000). Human Body Dynamics: Classical Mechanics and Human Movement. Springer. pp. 6–10. ISBN 0-387-98801-7.
  13. ^ Balaban, Naomi (2008). The Handy Anatomy Answer Book. Visible Ink Press. p. 61. ISBN 978-1-57859-190-9.
  14. ^ Stein, Lisa (2007). Body The Complete Human: How It Grows, How It Works, And How to Keep It Healthy And Strong. National Geographic Society. p. 73. ISBN 978-1-4262-0128-8.
  15. ^ Steele, D. Gentry; Claud A. Bramblett (1988). The Anatomy and Biology of the Human Skeleton. Texas A&M University Press. p. 4. ISBN 0-89096-300-2.
  16. ^ Schmiedeler, Edgar; Mary Rosa McDonough (1934). Parent and Child: An Introductory Study of Parent Education. D. Appleton-Century. p. 31.

External links

Appendicular skeleton

The appendicular skeleton is the portion of the skeleton of vertebrates consisting of the bones that support the appendages. The appendicular skeleton includes the skeletal elements within the limbs, as well as supporting pectoral and pelvic girdle. The word appendicular is the adjective of the noun appendage, which itself means a part that is joined to something larger.

Axial skeleton

The axial skeleton is the part of the skeleton that consists of the bones of the head and trunk of a vertebrate. In the human skeleton, it consists of 80 bones and is composed of six parts; the skull bones, the ossicles of the middle ear, the hyoid bone, the rib cage, sternum and the vertebral column. The axial skeleton together with the appendicular skeleton form the complete skeleton. Another definition of axial skeleton is the bones including the vertebrae, sacrum, coccyx, ribs, and sternum.

Bird anatomy

Bird anatomy, or the physiological structure of birds' bodies, shows many unique adaptations, mostly aiding flight. Birds have a light skeletal system and light but powerful musculature which, along with circulatory and respiratory systems capable of very high metabolic rates and oxygen supply, permit the bird to fly. The development of a beak has led to evolution of a specially adapted digestive system. These anatomical specializations have earned birds their own class in the vertebrate phylum.

Bobsleigh

Bobsleigh or bobsled is a winter sport in which teams of two or four teammates make timed runs down narrow, twisting, banked, iced tracks in a gravity-powered sleigh. The timed runs are combined to calculate the final score.

The various types of sleds came several years before the first tracks were built in St. Moritz, Switzerland, where the original bobsleds were adapted upsized luge/skeleton sleds designed by the adventurously wealthy to carry passengers. All three types were adapted from boys' delivery sleds and toboggans.

Competition naturally followed, and to protect the working class and rich visitors in the streets and byways of St Moritz, bobsledding was eventually banned from the public highway. In the winter of 1903/1904 the Badrutt family, owners of the historic Kulm Hotel and the Palace Hotel, allowed Emil Thoma to organise the construction of the first familiarly configured 'half-pipe' track in the Kulm Hotel Park, ending in the village of Cresta. It has hosted the sport during two Olympics and is still in use today.

International bobsleigh competitions are governed by the International Bobsleigh and Skeleton Federation, also known as FIBT from the French Fédération Internationale de Bobsleigh et de Tobogganing. National competitions are often governed by bodies such as the United States Bobsled and Skeleton Federation and Bobsleigh Canada Skeleton.

Coral

Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically live in compact colonies of many identical individual polyps. Corals species include the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.

A coral "group" is a colony of myriad genetically identical polyps. Each polyp is a sac-like animal typically only a few millimeters in diameter and a few centimeters in length. A set of tentacles surround a central mouth opening. An exoskeleton is excreted near the base. Over many generations, the colony thus creates a large skeleton characteristic of the species. Individual heads grow by asexual reproduction of polyps. Corals also breed sexually by spawning: polyps of the same species release gametes simultaneously over a period of one to several nights around a full moon.

Although some corals are able to catch small fish and plankton using stinging cells on their tentacles, most corals obtain the majority of their energy and nutrients from photosynthetic unicellular dinoflagellates in the genus Symbiodinium that live within their tissues. These are commonly known as zooxanthellae. Such corals require sunlight and grow in clear, shallow water, typically at depths less than 60 metres (200 ft). Corals are major contributors to the physical structure of the coral reefs that develop in tropical and subtropical waters, such as the enormous Great Barrier Reef off the coast of Queensland, Australia.

Other corals do not rely on zooxanthellae and can live in much deeper water, with the cold-water genus Lophelia surviving as deep as 3,300 metres (10,800 ft). Some have been found on the Darwin Mounds, northwest of Cape Wrath, Scotland, and others as far north as off the coast of Washington State and the Aleutian Islands.

Cytoskeleton

A cytoskeleton is present in the cytoplasm of all cells, including bacteria, and archaea. It is a complex, dynamic network of interlinking protein filaments that extends from the cell nucleus to the cell membrane. The cytoskeletal systems of different organisms are composed of similar proteins. In eukaryotes, the cytoskeletal matrix is a dynamic structure composed of three main proteins, which are capable of rapid growth or disassembly dependent on the cell's requirements.The structure, function and dynamic behavior of the cytoskeleton can be very different, depending on organism and cell type. Even within one cell the cytoskeleton can change through association with other proteins and the previous history of the network.A multitude of functions can be performed by the cytoskeleton. Its primary function is to give the cell its shape and mechanical resistance to deformation, and through association with extracellular connective tissue and other cells it stabilizes entire tissues. The cytoskeleton can also contract, thereby deforming the cell and the cell's environment and allowing cells to migrate. Moreover, it is involved in many cell signaling pathways: in the uptake of extracellular material (endocytosis), segregates chromosomes during cellular division, is involved in cytokinesis (the division of a mother cell into two daughter cells), provides a scaffold to organize the contents of the cell in space and for intracellular transport (for example, the movement of vesicles and organelles within the cell); and can be a template for the construction of a cell wall. Furthermore, it forms specialized structures, such as flagella, cilia, lamellipodia and podosomes.

A large-scale example of an action performed by the cytoskeleton is muscle contraction. This is carried out by groups of highly specialized cells working together. A main component in the cytoskeleton that helps show the true function of this muscle contraction is the microfilament. Microfilaments are composed of the most abundant cellular protein known as actin. During contraction of a muscle, within each muscle cell, myosin molecular motors collectively exert forces on parallel actin filaments. Muscle contraction starts from nerve impulses which then causes increased amounts of calcium to be released from the sarcoplasmic reticulum. Increases in calcium in the cytosol allows muscle contraction to begin with the help of two proteins, tropomyosin and troponin. Tropomyosin inhibits the interaction between actin and myosin, while troponin senses the increase in calcium and releases the inhibition. This action contracts the muscle cell, and through the synchronous process in many muscle cells, the entire muscle.

Exoskeleton

An exoskeleton (from Greek έξω, éxō "outer" and σκελετός, skeletós "skeleton") is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton (endoskeleton) of, for example, a human. In usage, some of the larger kinds of exoskeletons are known as "shells". Examples of animals with exoskeletons include insects such as grasshoppers and cockroaches, and crustaceans such as crabs and lobsters. The shells of certain sponges and the various groups of shelled molluscs, including those of snails, clams, tusk shells, chitons and nautilus, are also exoskeletons. Some animals, such as the tortoise, have both an endoskeleton and an exoskeleton.

Facial skeleton

The facial skeleton comprises the facial bones that may attach to build a portion of the skull. The remainder of the skull is the braincase.

In human anatomy and development, the facial skeleton is sometimes called the membranous viscerocranium, which comprises the mandible and dermatocranial elements that are not part of the braincase.

Human skeleton

The human skeleton is the internal framework of the body. It is composed of around 270 bones at birth – this total decreases to around 206 bones by adulthood after some bones get fused together. The bone mass in the skeleton reaches maximum density around age 21. The human skeleton can be divided into the axial skeleton and the appendicular skeleton. The axial skeleton is formed by the vertebral column, the rib cage, the skull and other associated bones. The appendicular skeleton, which is attached to the axial skeleton, is formed by the shoulder girdle, the pelvic girdle and the bones of the upper and lower limbs.

The human skeleton performs six major functions; support, movement, protection, production of blood cells, storage of minerals, and endocrine regulation.

The human skeleton is not as sexually dimorphic as that of many other primate species, but subtle differences between sexes in the morphology of the skull, dentition, long bones, and pelvis exist. In general, female skeletal elements tend to be smaller and less robust than corresponding male elements within a given population. The human female pelvis is also different from that of males in order to facilitate childbirth. Unlike most primates, human males do not have penile bones.

IBSF World Championships (bobsleigh and skeleton)

The IBSF World Championships (known as the FIBT World Championships until 2015), part of the International Bobsleigh and Skeleton Federation, have taken place on an annual basis in non-Winter Olympic years since 1930. A two-man event was included in 1931 with a combined championship occurring in 1947. Men's skeleton was introduced as a championship of its own in 1982 while women's bobsleigh and skeleton events were introduced in 2000. Both the women's bobsleigh and skeleton events were merged with the men's bobsleigh events at the 2004 championships. A mixed team event, consisting of one run each of men's skeleton, women's skeleton, 2-man bobsleigh, and 2-women bobsleigh debuted in 2007.

International Bobsleigh and Skeleton Federation

The International Bobsleigh and Skeleton Federation (IBSF), originally known by the French name Fédération Internationale de Bobsleigh et de Tobogganing (FIBT), is the international sports federation for bobsleigh and skeleton. It acts as an umbrella organization for 14 national bobsleigh and skeleton associations as of 2007. It was founded on 23 November 1923 by the delegates of Great Britain, France, Switzerland, Canada and the United States at the meeting of their first International Congress in Paris, France. In June 2015, it announced a name change from FIBT to IBSF. The federation's headquarters are in Lausanne, Switzerland.

List of bones of the human skeleton

The human skeleton of an adult consists of 206-208 bones, depending on the counting of the sternum (which may alternatively be included as the manubrium, body of sternum, and the xiphoid process) It is composed of 270 bones at birth, but later decreases to 80 bones in the axial skeleton and 126 bones in the appendicular skeleton. Many small supernumerary bones, such as some sesamoid bones, are not included in this count.

Lucy (Australopithecus)

Lucy is the common name of AL 288-1, several hundred pieces of bone fossils representing 40 percent of the skeleton of a female of the hominin species Australopithecus afarensis. In Ethiopia, the assembly is also known as Dinkinesh, which means "you are marvelous" in the Amharic language. Lucy was discovered in 1974 in Africa, near the village Hadar in the Awash Valley of the Afar Triangle in Ethiopia, by paleoanthropologist Donald Johanson of the Cleveland Museum of Natural History.The Lucy specimen is an early australopithecine and is dated to about 3.2 million years ago. The skeleton presents a small skull akin to that of non-hominin apes, plus evidence of a walking-gait that was bipedal and upright, akin to that of humans (and other hominins); this combination supports the view of human evolution that bipedalism preceded increase in brain size. A 2016 study proposes that Australopithecus afarensis was also to a large extent tree-dwelling, though the extent of this is debated."Lucy" acquired her name from the song "Lucy in the Sky with Diamonds" by The Beatles, which was played loudly and repeatedly in the expedition camp all evening after the excavation team's first day of work on the recovery site. After public announcement of the discovery, Lucy captured much public interest, becoming a household name at the time.

Lucy became famous worldwide, and the story of her discovery and reconstruction was published in a book by Johanson. Beginning in 2007, the fossil assembly and associated artifacts were exhibited publicly in an extended six-year tour of the United States; the exhibition was called Lucy's Legacy: The Hidden Treasures of Ethiopia. There was discussion of the risks of damage to the unique fossils, and other museums preferred to display casts of the fossil assembly. The original fossils were returned to Ethiopia in 2013, and subsequent exhibitions have used casts.

Pelvis

The pelvis (plural pelves or pelvises) is either the lower part of the trunk of the human body between the abdomen and the thighs (sometimes also called pelvic region of the trunk) or the skeleton embedded in it (sometimes also called bony pelvis, or pelvic skeleton).

The pelvic region of the trunk includes the bony pelvis, the pelvic cavity (the space enclosed by the bony pelvis), the pelvic floor, below the pelvic cavity, and the perineum, below the pelvic floor. The pelvic skeleton is formed in the area of the back, by the sacrum and the coccyx and anteriorly and to the left and right sides, by a pair of hip bones.

The two hip bones connect the spine with the lower limbs. They are attached to the sacrum posteriorly, connected to each other anteriorly, and joined with the two femurs at the hip joints. The gap enclosed by the bony pelvis, called the pelvic cavity, is the section of the body underneath the abdomen and mainly consists of the reproductive organs (sex organs) and the rectum, while the pelvic floor at the base of the cavity assists in supporting the organs of the abdomen.

In mammals, the bony pelvis has a gap in the middle, significantly larger in females than in males. Their young pass through this gap when they are born.

Skeleton (sport)

Skeleton is a winter sliding sport in which a person rides a small sled, known as a skeleton bobsled (or -sleigh), down a frozen track while lying face down and head-first. The sport and the sled may have been named from the bony appearance of the sled.Unlike other sliding sports of bobsleigh and luge, the race always involves single riders. Like bobsleigh, but unlike luge, the race begins with a running start from the opening gate at the top of the course. The skeleton sled is thinner and heavier than the luge sled, plus skeleton gives the rider more control making it safer than luge. Skeleton is the slowest of the three sliding sports, as skeleton's face down head-first riding position is less aerodynamic than luge's face up, feet-first ride.Previously, skeleton appeared in the Olympic program in St. Moritz, Switzerland, in 1928 and again in 1948. It was added permanently to the Olympic program for the 2002 Winter Olympics, at which stage a women's race was added.

During elite racing the rider experiences accelerations up to 5 g and reaches speeds over 130 km/h (80 mph).

Skeleton Crew

Skeleton Crew is a collection of short fiction by American writer Stephen King, published by Putnam in June 1985. A limited edition of a thousand copies was published by Scream/Press in October 1985 (ISBN 978-0910489126), illustrated by J. K. Potter, containing an additional short story, "The Revelations of 'Becka Paulson", which had originally appeared in Rolling Stone magazine (July 19 – August 2, 1984), and was later incorporated into King's 1987 novel The Tommyknockers. The original title of this book was Night Moves.

Skull

The skull is a bony structure that forms the head in vertebrates. It supports the structures of the face and provides a protective cavity for the brain. The skull is composed of two parts: the cranium and the mandible. In the human, these two parts are the neurocranium and the viscerocranium or facial skeleton that includes the mandible as its largest bone. The skull forms the anterior most portion of the skeleton and is a product of cephalisation—housing the brain, and several sensory structures such as the eyes, ears, nose, and mouth. In humans these sensory structures are part of the facial skeleton.

Functions of the skull include protection of the brain, fixing the distance between the eyes to allow stereoscopic vision, and fixing the position of the ears to enable sound localisation of the direction and distance of sounds. In some animals such as horned ungulates, the skull also has a defensive function by providing the mount (on the frontal bone) for the horns.

The English word "skull" is probably derived from Old Norse "skulle", while the Latin word cranium comes from the Greek root κρανίον (kranion).

The skull is made up of a number of fused flat bones, and contains many foramina, fossae, processes, and several cavities or sinuses. In zoology there are openings in the skull called fenestrae.

Tarsus (skeleton)

The tarsus is a cluster of seven articulating bones in each foot situated between the lower end of tibia and fibula of the lower leg and the metatarsus. It is made up of the midfoot (cuboid, medial, intermediate, and lateral cuneiform, and navicular) and hindfoot (talus and calcaneus).

The tarsus articulates with the bones of the metatarsus, which in turn articulate with the proximal phalanges of the toes. The joint between the tibia and fibula above and the tarsus below is referred to as the ankle joint.

In humans the largest bone in the tarsus is the calcaneus, which is the weight-bearing bone within the heel of the foot.

Thorax

The thorax or chest (from the Greek θώραξ thorax "breastplate, cuirass, corslet" via Latin: thorax) is a part of the anatomy of humans and various other animals located between the neck and the abdomen. The thorax includes the thoracic cavity and the thoracic wall. It contains organs including the heart, lungs, and thymus gland, as well as muscles and various other internal structures. Many diseases may affect the chest, and one of the most common symptoms is chest pain.

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