The least variable part of the spinalis muscle is the spinalis thoracis, which is a member of the erector spinae group in the back muscles.
The least variable of the different parts of the spinalis muscle is the spinalis thoracis. The spinalis muscle group, including spinalis capitis, spinalis cervicis, spinalis thoracis, is a part of the erector spinae, which plays a crucial role in extending and laterally flexing the vertebral column. Among the components of the spinalis group, the spinalis thoracis shows the least variability.
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