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The sacrum ( or ; plural: ''sacra'' or ''sacrums'';〔(Oxford Dictionaries ) and (Webster's New College Dictionary ) (2010) admit the plural ''sacrums'' alongside ''sacra''; (The American Heritage Dictionary ), (Collins Dictionary ) and (Webster's Revised Unabridged Dictionary ) (1913) give ''sacra'' as the only plural.〕 Latin ''os sacrum''〔"sacred bone", translation of Greek ἱερόν ὀστέον, supposedly so called because of its role in ancient animal sacrifice. 〕) in human anatomy is a large, triangular bone at the base of the spine, that forms by the fusing of sacral vertebrae S1S5, between 18 and 30 years of age.〔 〕 The sacrum articulates (forms a joint with) with four other bones. It is situated at the upper, back part of the pelvic cavity, where it is anatomically inserted between the two hip bones (ilium). The two lateral projections of the sacrum are called the alae (wings), and articulate with the ilium at the L-shaped sacroiliac joints. The upper part of the sacrum connects with the last lumbar vertebra, and its lower part with the coccyx (tailbone) via the sacral and coccygeal cornu. The sacrum has three different surfaces which are shaped to accommodate surrounding pelvic structures. Overall it is concave (curved upon itself). The base of the sacrum (the broadest and uppermost part) is tilted forward as the sacral promontory internally. The central part is curved outward toward the posterior, allowing greater room for the pelvic cavity. In all other quadrupedal vertebrates, the pelvic vertebrae undergo a similar developmental process to form a sacrum in the adult, even while the bony tail (caudal vertebrae) remain unfused. The number of sacral vertebrae varies slightly. A horse will fuse S1S5, but a dog will fuse S1S3. For example, the rat fuses four pelvic vertebrae between their lumbar and the caudal vertebrae of their tail. The ''Stegosaurus '' dinosaur had a greatly enlarged neural canal in the sacrum, characterized as a "posterior brain case". ==Name== English ''sacrum'' was introduced as a technical term in anatomy in the mid-18th century, as a shortening of the Late Latin name ''os sacrum'' "sacred bone", itself a translation of Greek ἱερόν ὀστέον, the term found in the writings of Galen.〔〔Hyrtl, J. (1880). ''Onomatologia Anatomica. Geschichte und Kritik der anatomischen Sprache der Gegenwart.'' Wien: Wilhelm Braumüller. K.K. Hof- und Unversitätsbuchhändler.〕〔Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with the assistance of. Roderick McKenzie.'' Oxford: Clarendon Press.〕〔Anderson, D.M. (2000). ''Dorland’s illustrated medical dictionary'' (29th edition). Philadelphia/London/Toronto/Montreal/Sydney/Tokyo: W.B. Saunders Company.〕〔His, W. (1895). ''Die anatomische Nomenclatur. Nomina Anatomica. Der von der Anatomischen Gesellschaft auf ihrer IX. Versammlung in Basel angenommenen Namen''. Leipzig: Verlag Veit & Comp.〕〔Federative Committee on Anatomical Terminology (FCAT) (1998). ''Terminologia Anatomica''. Stuttgart: Thieme〕〔Lewis, C.T. & Short, C. (1879). ''A Latin dictionary founded on Andrews' edition of Freund's Latin dictionary.'' Oxford: Clarendon Press.〕 Prior to the adoption of ''sacrum'', the bone was also called ''holy bone'' in English,〔Schreger, C.H.Th. (1805). ''Synonymia anatomica. Synonymik der anatomischen Nomenclatur.'' Fürth: im Bureau für Literatur.〕 paralleling German ''heiliges Bein'' or ''Heiligenbein'' (alongside ''Kreuzbein''〔"cross bone", also of unclear origin. According to Grimm, ''Deutsches Wörterbuch'' (("Kreuz", meaning 8a )), ''Kreuz'' "cross" is used of the sacral area of the spine, but also of the spine as a whole, with usage examples from the 17th-century (Christian Weise, ''Isaacs Opferung'', 1682, 3.11). ''Notabilia Venatoris'' by Hermann Friedrich von Göchhausen (1710) and ''Teutscher Jäger'' by Johann Friedrich von Flemming (1719, p. 94) also give ''kreuz'' as hunting terminology for a specific bone of the stag.〕) and Dutch ''heiligbeen''.〔〔Foster, F.D. (1891-1893). ''An illustrated medical dictionary. Being a dictionary of the technical terms used by writers on medicine and the collateral sciences, in the Latin, English, French, and German languages.'' New York: D. Appleton and Company.〕〔Everdingen, J.J.E. van, Eerenbeemt, A.M.M. van den (2012). ''Pinkhof Geneeskundig woordenboek'' (12de druk). Houten: Bohn Stafleu Van Loghum.〕 The origin of Galen's term is unclear. Supposedly the sacrum was the part of an animal offered in sacrifice (since the sacrum is the seat of the organs of procreation).〔(Online Etymology Dictionary )〕 Others attribute the adjective ἱερόν to the ancient belief that this specific bone would be indestructible.〔 As the Greek adjective ἱερός may also mean "strong", it has also been suggested that ''os sacrum'' is a mistranslation of a term intended to mean "the strong bone". This is supported by the alternative Greek name μέγας σπόνδυλος by the Greeks, translating to "large vertebra", translated into Latin as ''vertebra magna''.〔〔Hyrtl, J. (1875). ''Lehrbuch der Anatomie des Menschen. Mit Rücksicht auf physiologische Begründung und praktische Anwendung.'' (Dreizehnte Auflage). Wien: Wilhelm Braumüller K.K. Hof- und Universitätsbuchhändler.〕 In Classical Greek the bone was known as κλόνις (Latinized ''clonis''); this term is cognate to Latin ''clunis'' "buttock", Sanskrit ' "haunch" and Lithuanian ''šlaunis'' "hip, thigh".〔used by Antimachus; see (Henry George Liddell, Robert Scott, A Greek-English Lexicon )〕〔Kraus, L.A. (1844). ''Kritisch-etymologisches medicinisches Lexikon'' (Dritte Auflage). Göttingen: Verlag der Deuerlich- und Dieterichschen Buchhandlung.〕 The Latin word is found in the alternative Latin name of the sacrum, ''ossa clunium'', as it were "bones of the buttocks".〔 Due to the fact that the os sacrum is broad and thick at its upper end,〔 the sacrum is alternatively called ''os latum'', "broad bone".〔〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Sacrum」の詳細全文を読む スポンサード リンク
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