MEHAU KULYK / SCIENCE PHOTO LIBRARY MEHAU KULYK / SCIENCE PHOTO LIBRARY
Spinal vertebra. Historical artwork of a vertebra (spinal bone) seen from above. The rear of the spine is at top. This is a lumbar vertebra, one from the lower back. There are 24 vertebra in the main spinal column. Each one consists of a block of bone (bottom) that carries the weight supported by the spine, plus protruding bits of bone called processes (top). The processes are where the back ligaments and muscles attach to the spine. A disc of cartilage would fit over the block of bone at bottom, cushioning the spine. The spinal cord (not shown) would pass down centre, between the main part of the vertebra and its processes. This space is the vertebral canal, which is triangular in the lumbar region. There are five lumbar vertebrae.
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