Lumbar has several meanings in the field of medicine:

1. Pertaining to the loin, part of the back between the
lowest pair of ribs of the thorax (chest) and the top of the
pelvis. The pelvis is a massive bone made of hip bones
on each side and the front, while the back part is made of
the sacrum (a triangular bone) and coccyx (a beak
shaped bone).

2. Pertaining to the part of the vertebrae (bones that form
an opening in which the spinal cord passes) that are in
the area of the loin (see above for description). There are
five lumbar vertebrae, known as L1 through L5.
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The lumbar vertebrae are located between the thoracic vertebrae and sacral vertebrae.
The thoracic vertebrae are located near the thorax (chest) area. Sacral refers to the
sacrum, which is discussed above.

An example of how lumbar is used in this context is a lumbar puncture (also known as a
spinal tap), which is a procedure in which a needle is inserted into a space inside the
spinal canal for the purpose of removing some of the cerebrospinal fluid. Cerebrospinal
fluid is the fluid that cushions the brain and spinal cord. The spinal canal is the space
between the spinal cord and the bony structure that surrounds it.

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3. Pertaining to sides next to the middle of the belly and above the ilium. The ilium is a large bone that
makes up the upper part of the hip. Lumbar is most often used to refer to the first two meanings, listed
above. Lumbar comes from the Latin word "lumbus" meaning "loin."