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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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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.



A triangular bone, consisting in humans of five fused vertebrae, located below the last lumbar vertebra, above the coccyx, and between the hipbones.


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
References in periodicals archive ?
Sacral index was measured by taking the breadth and length of individual sacrum with the help of Vernier Digital Caliper and adopting the method as demonstrated in Hrdlicka's Practical Anthropometry.
Thus, understanding the morphological variations of sacrum and coccyx is imperative.
Poznanski, "Fatigue fractures of the sacrum in children: two case reports and a review of the literature," Skeletal Radiology, vol.
We cannot prove that the development of the osteomyelitis of the sacrum was unequivocally based on the arthroscopy of the knee, but we consider hematogenous spread from the knee to be very likely.
In the chapter about back pain, we learn that the sacrum can often be the cause.
The veteran celebrity and singer had an accident on holiday in California, causing a fractured sacrum.
According to the findings, the anatomy of Oreopithecus lumbar vertebrae and sacrum is unlike that of humans, and more similar to apes, indicating that it is incompatible with the functional demands of walking upright as a human does.
Generally, the sacrum comprises five rudimentary fused vertebrae, but numerous anatomical variations have been reported.
The radiographs were normal, and the bone scan revealed an increased uptake on the right side of the sacrum adjacent to the sacroiliac joint.
A computed tomography (CT) scan of the abdomen and pelvis showed a presacral fluid collection with a fistula between the pouch and the sacrum (Fig.
The key to understanding the relationship between the pelvis and lumbar spine is that the lumbar spine sits on the sacrum.