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see spinal columnspinal column,
bony column forming the main structural support of the skeleton of humans and other vertebrates, also known as the vertebral column or backbone. It consists of segments known as vertebrae linked by intervertebral disks and held together by ligaments.
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The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



in terrestrial vertebrate animals and in man, one or several vertebrae that provide a strong connection between the iliac bones of the pelvis and the axial skeleton. The sacrum was formed as a result of the progressive development of the posterior extremities and their important role in locomotion. True sacral vertebrae (on which, if only in the embryo, there are sacral ribs that subsequently grow together with the transverse processes of the vertebrae) are distinguished from those that enter into the composition of the sacrum secondarily in order to reinforce it.

Present-day amphibians have one sacral vertebra, and reptiles have two (fossil forms often had more). In birds with two true sacral vertebrae, the anterior caudal, all the lumbar, and one or two of the last thoracic vertebrae are grown together to form a single bone, the synsacrum, out of ten or 12 vertebrae. In mammals, up to ten vertebrae are grown together in the sacrum; only one or two are true sacral vertebrae, and the rest are the anterior caudal vertebrae. When there is secondary disappearance of the posterior extremities (for example, in snakes and whales), the sacral region of the spine loses its function and is not differentiated.

In humans the sacrum is formed of five vertebrae, which merge in adults into a single sacral bone (os sacrum), which posteriorly closes the pelvic girdle.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


A triangular bone, consisting in humans of five fused vertebrae, located below the last lumbar vertebra, above the coccyx, and between the hipbones.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


1. (in man) the large wedge-shaped bone, consisting of five fused vertebrae, in the lower part of the back
2. the corresponding part in some other vertebrates
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
The prevalence of the lumbarization of first sacral vertebra varies from 4.2% to 9.2% in different populations by origin.
[11] Thus sacralization of fifth lumbar vertebra and lumbarization of first sacral vertebra are caused by the border shifts, cranial shift resulting in the sacralization of fifth lumbar vertebra and a caudal shift resulting in the lumbarization of first sacral segment.
Measurement of maximum length of sacrum was recorded by the distance from antero-superior margin of promontory to the middle of anteroinferior margin of the last sacral vertebra. Maximum breadth of sacrum was measured by taking two points at the upper part of auricular surface anteriorly.
Partial or complete fusion of fifth lumbar vertebrae with first sacral vertebra is called sacralisation.
Location of the apex of sacral hiatus in relation to level of sacral vertebra varied from S2 to S5 vertebra level.
Wellik & Capecchi (2005) reported Genetic factors have also been implicated in the development if transitional vertebra these include Mutations in the HOX 10 and HOX 11 genes results can alter the normal pattering of lumbar and sacral vertebra leading to lumbosacral transition vertebrae.
At the cranial end of sacrum there is fifth lumbar vertebra, which when fused with the first sacral vertebra is known as sacralization of lumbar vertebra.