The ilium () (plural ilia) is the uppermost and largest part of the

hip bone The hip bone (os coxae, innominate bone, pelvic bone or coxal bone) is a large flat bone, constricted in the center and expanded above and below. In some vertebrates (including humans before puberty) it is composed of three parts: the Ilium (bone), ...

, and appears in most

vertebrates Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

including

mammals Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

and

birds Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

, but not

bony fish Osteichthyes (), popularly referred to as the bony fish, is a diverse superclass of fish that have skeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes, which have skeletons primarily composed of cartilag ...

. All reptiles have an ilium except

snakes Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more joi ...

, although some snake species have a tiny bone which is considered to be an ilium. The ilium of the

human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...

is divisible into two parts, the body and the wing; the separation is indicated on the top surface by a curved line, the arcuate line, and on the external surface by the margin of the

acetabulum The acetabulum (), also called the cotyloid cavity, is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint. Structure There are three bones of the ''os coxae'' (hip bone) that c ...

. The name comes from the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

(''

ile Ile may refer to: * iLe, a Puerto Rican singer * Ile District (disambiguation), multiple places * Ilé-Ifẹ̀, an ancient Yoruba city in south-western Nigeria * Interlingue (ISO 639:ile), a planned language * Isoleucine, an amino acid * Anothe ...

'', ''ilis''), meaning "groin" or "flank".

Structure

The ilium consists of the body and

wing A wing is a type of fin that produces lift while moving through air or some other fluid. Accordingly, wings have streamlined cross-sections that are subject to aerodynamic forces and act as airfoils. A wing's aerodynamic efficiency is expres ...

. Together with the

ischium The ischium () form ...

and pubis, to which the ilium is connected, these form the pelvic bone, with only a faint line indicating the place of union. The body ( la, corpus) forms less than two-fifths of the

; and also forms part of the acetabular fossa. The internal surface of the body is part of the wall of the

lesser pelvis The pelvic cavity is a body cavity that is bounded by the bones of the pelvis. Its oblique roof is the pelvic inlet (the superior opening of the pelvis). Its lower boundary is the pelvic floor. The pelvic cavity primarily contains the reproducti ...

and gives origin to some fibers of the

obturator internus The internal obturator muscle or obturator internus muscle originates on the medial surface of the obturator membrane, the ischium near the membrane, and the rim of the pubis. It exits the pelvic cavity through the lesser sciatic foramen. The i ...

. The

( la, ala) is the large expanded portion which bounds the

greater pelvis The pelvic cavity is a body cavity that is bounded by the bones of the pelvis. Its oblique roof is the pelvic inlet (the superior opening of the pelvis). Its lower boundary is the pelvic floor. The pelvic cavity primarily contains the reproducti ...

laterally. It has an external and an internal surface, a crest, and two borders—an anterior and a posterior.

Biiliac width

In humans, biiliac width is an anatomical term referring to the widest measure of the pelvis between the outer edges of the upper iliac bones. Biiliac width has the following common synonyms:

pelvic bone The hip bone (os coxae, innominate bone, pelvic bone or coxal bone) is a large flat bone, constricted in the center and expanded above and below. In some vertebrates (including humans before puberty) it is composed of three parts: the ilium, ischi ...

width, biiliac breadth, intercristal breadth/width, bi-iliac breadth/width and biiliocristal breadth/width. It is best measured by anthropometric

caliper A caliper (British spelling also calliper, or in plurale tantum sense a pair of calipers) is a device used to measure the dimensions of an object. Many types of calipers permit reading out a measurement on a ruled scale, a dial, or a digital dis ...

s (an anthropometer designed for such measurement is called a pelvimeter). Attempting to measure biiliac width with a

tape measure A tape measure or measuring tape is a flexible ruler used to measure length or distance. It consists of a ribbon of cloth, plastic, fibre glass, or metal strip with linear measurement markings. It is a common measuring tool. Its design all ...

along a curved surface is inaccurate. The biiliac width measure is helpful in

obstetrics Obstetrics is the field of study concentrated on pregnancy, childbirth and the postpartum period. As a medical specialty, obstetrics is combined with gynecology under the discipline known as obstetrics and gynecology (OB/GYN), which is a surgi ...

because a pelvis that is significantly too small or too large can have complications. For example, a large baby or a small pelvis often lead to death unless a

caesarean section Caesarean section, also known as C-section or caesarean delivery, is the surgical procedure by which one or more babies are delivered through an incision in the mother's abdomen, often performed because vaginal delivery would put the baby or mo ...

is performed. It is also used by

anthropologists An anthropologist is a person engaged in the practice of anthropology. Anthropology is the study of aspects of humans within past and present societies. Social anthropology, cultural anthropology and philosophical anthropology study the norms and v ...

to estimate body mass.

Other animals

Dinosaurs

The

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

Dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

ia is divided into the

Saurischia Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...

and

Ornithischia Ornithischia () is an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek s ...

based on hip structure, including importantly that of the ilium. In both saurischians and ornithischians, the ilium extends laterally to both sides from the axis of the body. The other two hip bones, the

ischium The ischium () form ...

and the pubis, extend ventrally down from the ilium towards the belly of the animal. The

, which can be thought of as a "hip-socket", is an opening on each side of the pelvic girdle formed where the ischium, ilium, and pubis all meet, and into which the head of the femur inserts. The orientation and position of the acetabulum is one of the main morphological traits that caused dinosaurs to walk in an upright posture with their legs directly underneath their bodies. The brevis fossa is a deep groove in the underside of the postacetabular process, the rear part of the ilium. The brevis shelf is the bony ridge at the inner side of the ''fossa'', the bone wall forming the internal face of the rear part of the ilium, which functions as an attachment area for a tail muscle, the ''

musculus caudofemoralis brevis Musculus may refer to: * Andreas Musculus (1514–1581), German Lutheran theologian *Heinrich Musculus (b. 1868), Swedish-Norwegian businessperson *Wolfgang Musculus Wolfgang Musculus, born "Müslin" or "Mauslein", (10 September 1497 – 30 Augus ...

''.Martin, A.J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. pg. 299-300. . Often, close to the hip-socket the lower edge of the outer face of the postacetabular process is positioned higher than the edge of the brevis shelf, exposing the latter in side view. Ornithischia pelvis structure.svg, Ornithischian pelvic structure (left side) Saurischia pelvis structure.svg, Saurischian pelvic structure (left side).

History

The 'English' name ''ilium'' as bone of the ''pelvis'' can be traced back to the writings of anatomists

Andreas Vesalius Andreas Vesalius (Latinized from Andries van Wezel) () was a 16th-century anatomist, physician, and author of one of the most influential books on human anatomy, ''De Humani Corporis Fabrica Libri Septem'' (''On the fabric of the human body'' '' ...

, who coined the expression ''os ilium''.Hyrtl, J. (1880). ''Onomatologia Anatomica. Geschichte und Kritik der anatomischen Sprache der Gegenwart.'' Wien: Wilhelm Braumüller. K.K. Hof- und Universitätsbuchhändler. In this expression ''ilium'' can be considered as the genitive plural of the nominative singular of the noun ''ile''. Ile in classical Latin can refer to the ''flank of the body'',Lewis, C.T. & Short, C. (1879). ''A Latin dictionary founded on Andrews' edition of Freund's Latin dictionary.'' Oxford: Clarendon Press. or to the ''groin'', or the ''part of the abdomen from the lowest ribs to the pubes''. Ile is usually encountered as plural (''ilia'') in classical Latin. The ''os ilium'' can literally be translated as ''bone'' (Latin: ''os'' ) ''of the flanks''. More than a millennium earlier the ''ossa ilium'' were described by the Greek physician

Galen Aelius Galenus or Claudius Galenus ( el, Κλαύδιος Γαληνός; September 129 – c. AD 216), often Anglicized as Galen () or Galen of Pergamon, was a Greek physician, surgeon and philosopher in the Roman Empire. Considered to be one of ...

, and referred to as, with a quite similar expression, τά πλατέα λαγόνων ὀστᾶ, ''the flat bones of the flanks'', with λαγών for ''flank''.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. In anatomic Latin, the expression ''os lagonicum''Kossmann, R. (1895). Die gynäcologische Anatomie und ihre zu Basel festgestellte Nomenclatur. ''Monatsschrift für Geburtshülfe und Gynaekologie'', 2 (6), 447-472. can also be found, based on Ancient Greek λαγών. In

modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek (, ), refers collectively to the dialects of the Greek language spoken in the modern era, including the official standardized form of the ...

the nominalized adjective λαγόνιοSchleifer, S.K. (Ed.) (2011). ''Corpus humanum, The human body, Le corps humain, Der menschliche Körper, Il corpo umano, El cuerpo humano, Ciało człowieka, Människokroppen, Menneskekroppen, Τό ανθρώπινο σῶμα, ЧЕЛОВЕК.'' FKG. is used to refer to the ''os ilium''. In Latin and Greek it is not uncommon to nominalize adjectives, e.g. ''stimulantia'' from ''remedia stimulantia''Arnaudov, G.D. (1964). ''Terminologia medica polyglotta. Latinum-Bulgarski-Russkij-English-Français-Deutsch.'' Sofia: Editio medicina et physcultura. or ὁ ἐγκέφαλος from ὁ ἐγκέφαλος μυελός.Kraus, L.A. (1844). ''Kritisch-etymologisches medicinisches Lexikon'' (Dritte Auflage). Göttingen: Verlag der Deuerlich- und Dieterichschen Buchhandlung. The name ''ilium'' as used in EnglishDorland, W.A.N. & Miller, E.C.L. (1948). ''The American illustrated medical dictionary.’’ (21st edition). Philadelphia/London: W.B. Saunders Company.Dirckx, J.H. (Ed.) (1997).''Stedman’s concise medical dictionary for the health professions.'' (3rd edition). Baltimore: Williams & Wilkins. can not be considered as nominalized adjective derived from the full Latin expression ''os ilium'', as ''ilium'' in this expression is a genitive plural of a noun and not a nominative singular of an adjective. The form ''ilium'' in English is however thought to be derived from the Latin word ''ilium'',Klein, E. (1971). A comprehensive etymological dictionary of the English language. Dealing with the origin of words and their sense development thus illustration the history of civilization and culture. Amsterdam: Elsevier Science B.V. an orthographic variant in Latin of ''ile'', ''flank'' or ''groin''. Whereas the expression of Andreas Vesalius ''os ilium'' appropriately expresses ''bone of the flanks'', the sole term ''ilium'' as used in English, lacks this precision and has to be literally translated as ''groin'' or ''flank''. There exists however in classical Latin an adjective ''ilius/ilia/ilium''. This adjective however means not ''with respect to the flanks'', but ''Trojan''. ''Troy'' is referred to in classical Latin as ''Ilium'', ''Ilion'' or ''Ilios''Wageningen, J. van & Muller, F. (1921). ''Latijnsch woordenboek.'' (3de druk). Groningen/Den Haag: J.B. Wolters’ Uitgevers-Maatschappij and in ancient Greek as Ἴλιον or Ἴλιος. The first editions of the official Latin nomenclature, ''

Nomina Anatomica ''Nomina Anatomica'' (''NA'') was the international standard on human anatomic terminology from 1895 until it was replaced by ''Terminologia Anatomica'' in 1998. In the late nineteenth century some 30,000 terms for various body parts were in use ...

'' of the first 80 years (first in 1895) used the Vesalian expression ''os ilium''.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.Kopsch, F. (1941). ''Die Nomina anatomica des Jahres 1895 (B.N.A.) nach der Buchstabenreihe geordnet und gegenübergestellt den Nomina anatomica des Jahres 1935 (I.N.A.)'' (3. Auflage). Leipzig: Georg Thieme Verlag.Stieve, H. (1949). ''Nomina Anatomica. Zusammengestellt von der im Jahre 1923 gewählten Nomenklatur-Kommission, unter Berücksichtigung der Vorschläge der Mitglieder der Anatomischen Gesellschaft, der Anatomical Society of Great Britain and Ireland, sowie der American Association of Anatomists, überprüft und durch Beschluß der Anatomischen Gesellschaft auf der Tagung in Jena 1935 endgúltig angenommen.'' (4th edition). Jena: Verlag Gustav Fischer.Donáth, T. & Crawford, G.C.N. (1969). ''Anatomical dictionary with nomenclature and explanatory notes.'' Oxford/London/Edinburgh/New York/Toronto/Syney/Paris/Braunschweig: Pergamon Press.International Anatomical Nomenclature Committee (1966). ''Nomina Anatomica''. Amsterdam: Excerpta Medica Foundation.International Anatomical Nomenclature Committee (1977). ''Nomina Anatomica, together with Nomina Histologica and Nomina Embryologica''. Amsterdam-Oxford: Excerpta Medica. In the subsequent editions from 1983International Anatomical Nomenclature Committee (1983). ''Nomina Anatomica, together with Nomina Histologica and Nomina Embryologica''. Baltimore/London: Williams & Wilkins and 1989International Anatomical Nomenclature Committee (1989). ''Nomina Anatomica, together with Nomina Histologica and Nomina Embryologica''. Edinburgh: Churchill Livingstone. the expression ''os ilium'' was altered to ''os ilii''. This latter expression supposes a genitive singular of the alternate noun ''ilium'' instead of a genitive plural of the noun ''ile''. Quite inconsistently, in the 1983 edition of the ''Nomina Anatomica'' the genitive plural of ''ile'' (instead of ''ilium'') is still being used in such expressions as ''vena circumflexa ilium superficialis''. In the current 1998 edition of the ''Nomina Anatomica'', rebaptized as ''

Terminologia Anatomica ''Terminologia Anatomica'' is the international standard for human anatomical terminology. It is developed by the Federative International Programme on Anatomical Terminology, a program of the International Federation of Associations of Anatomis ...

'', the expression ''os ilium'' is reintroduced and ''os ilii'' deleted.

Additional images

Pelvic girdle illustration.svg, Pelvic girdle Gray236.png, Right hip bone. Internal surface. Gray235.png, Right hip bone. External surface. (Body of ilium is the top of the blue circle in the center, and the wing of the ilium is the portion above that. Crest of ilium is labeled at top.) Gray237.png, Plan of ossification of the hip bone. Gray341.png, Left hip-joint, opened by removing the floor of the acetabulum from within the pelvis. Skeletal pelvis-pubis.svg, Pelvis

References

External links

* * {{Authority control Bones of the pelvis he:אגן#כסל