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but it is especially L3 having a posterior arc very developped which
is useful as a point of support with ear-thorn-bush in its action
of rachis erecting as soon as L3 is fixed to pelvis by the intermediary
of iliac beams of longissimus.
Located
at the node of lumbar lordosis with plates parallel between them,
L3 is the first really mobile vertebra of the lumbar rachis. L4 and
L5 strongly moored to the pelvis forming more a static transition
than a dynamic one.
The
use ( we will see it further on ) of L4 and L5 for dynamic
purposes causes lumbagos by constraint on the posterior articulars,
wear of the intervertebral discs or slipped discs.
For
better understanding of the operation of the muscular system characterizing
the dynamic attitude,we will initially describe the system being used
for the rachis erection starting from L3 , then the system being used
for the mooring of the rachis below L3.
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