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Sacrum

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	Sacrum
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	Topics Sacrum Topic Home The sacrum is a large, triangular bone at the base of the spineVertebral column Summary In human anatomy, the vertebral column is a column of vertebrae situated in the dorsal aspect of the torso.... and at the upper and back part of the pelvic cavityPelvic cavity The Pelvic cavity is a body cavity that is bounded by the bones of the pelvis and which primarily contains reproductive orga... , where it is inserted like a wedge between the two hip bones. Its upper part connects with the last lumbar vertebraLumbar vertebrae The lumbar vertebrae are the largest segments of the movable part of the vertebral column, and can be distinguished by the a... , and bottom part with the coccyxCoccyx The coccyx, commonly referred to as the tailbone, is the final segment of the human vertebral column, of three to five f... (tailbone). It is curved upon itself and placed obliquely (that is, tilted forward). It is kyphotic — that is, concave facing forwards. The base projects forward as the sacral promontorySacral promontory The sacral promontory is the anatomical term for the superiormost portion of the sacrum.... internally, and articulates with the last lumbar vertebra to form the prominent sacrovertebral angleSacrovertebral angle Overview The sacrum is curved upon itself and placed very obliquely, its base projecting forward and forming the prominent sacrovertebra... . The central part is curved outward towards the posterior, allowing greater room for the pelvic cavityPelvic cavity The Pelvic cavity is a body cavity that is bounded by the bones of the pelvis and which primarily contains reproductive orga... . Etymology The name is derived from the LatinLatin Latin is an ancient Indo-European language originally spoken in Latium, the region immediately surrounding Rome.... sacer, "sacred", a translation of the GreekGreek language Greek has a documented history of 3,500 years, the longest of any single language within the Indo-European family.... hieron (osteon), meaning sacred or strong bone. This is supposedly because the sacrum was the part of an animal offered in sacrificeSacrifice Sacrifice is commonly known as the practice of offering food, or the lives of animals or people to the gods, as an act of pr... . In Slavic languagesSlavic languages The Slavic languages , a group of closely related languages of the Slavic peoples and a subgroup of Indo-European languages,... and in GermanGerman language German is a West Germanic language.... this bone is called the "cross bone". Parts The pelvic surface of the sacrumPelvic surface of sacrum The pelvic surface of sacrum is concave from above downward, and slightly so from side to side.... is concave from above downward, and slightly so from side to side. The dorsal surface of the sacrumDorsal surface of sacrum The dorsal surface of sacrum is convex and narrower than the pelvic.... is convex and narrower than the pelvic. The lateral surface of the sacrumLateral surface of sacrum The lateral surface of sacrum is broad above, but narrowed into a thin edge below.... is broad above, but narrowed into a thin edge below. The base of the sacrumBase of the sacrum The base of the sacrum, which is broad and expanded, is directed upward and forward.... , which is broad and expanded, is directed upward and forward. The apex (apex oss. sacri) is directed downward, and presents an oval facet for articulation with the coccyx. The vertebral canal (canalis sacralis; sacral canal) runs throughout the greater part of the bone; above, it is triangular in form; below, its posterior wall is incomplete, from the non-development of the laminae and spinous processes. It lodges the sacral nerves, and its walls are perforated by the anterior and posterior sacral foramina through which these nerves pass out. Articulations The sacrum articulates with four bones: the last lumbar vertebra above the coccyxCoccyx The coccyx, commonly referred to as the tailbone, is the final segment of the human vertebral column, of three to five f... (tailbone) below the hip boneHip bone The hip bone, innominate bone or coxal bone is a large, flattened, irregularly shaped bone, constricted in the c... on either side Rotatation of the sacrum forward a few degrees vis-à-vis the iliaIlium (bone) The ilium of the pelvis is divisible into two parts, the body and the ala; the separation is indicated on the internal surfa... is sometimes called "nutationNutation Summary Nutation is a slight irregular motion in the axis of rotation of a largely axially symmetric object, such as a gyroscope or... ", and the reverse motion "counter-nutation." It is called the sacrum when referred to all of the parts combined, but sacral vertebrae when referred individually. Sexual dimorphism The sacrum is noticeably sexually dimorphicSexual dimorphism Sexual dimorphism is the systematic difference in form between individuals of different sex in the same species.... (differently-shaped in males and females). In the female the sacrum is shorter and wider than in the male; the lower half forms a greater angle with the upper; the upper half is nearly straight, the lower half presenting the greatest amount of curvature. The bone is also directed more obliquely backward; this increases the size of the pelvic cavity and renders the sacrovertebral angle more prominent. In the male the curvature is more evenly distributed over the whole length of the bone, and is altogether greater than in the female. Variations The sacrum, in some cases, consists of six pieces ; occasionally the number is reduced to four . The bodies of the first and second vertebrae may fail to unite. Sometimes the uppermost transverse tubercles are not joined to the rest of the ala on one or both sides, or the sacral canal may be open throughout a considerable part of its length, in consequence of the imperfect development of the laminae and spinous processes. The sacrum also varies considerably with respect to its degree of curvature. Additional images See also Bone terminologyBone Bone, also called osseous tissue, is a type of hard endoskeletal connective tissue found in many vertebrate animals.... Terms for anatomical location PelvimetryPelvimetry Pelvimetry is the assessment of the female pelvis is relation to the birth of a baby.... External links