The spinalis thoracis originates from which spinous processes?

• A. Spinous processes of T1-T8
• B. Spinous processes of L2-L5
• C. Spinous processes of C7-T1
• D. Transverse processes of L1-L3

Answer: (B)

Spinalis thoracis is the most medial part of the erector spinae, and its job is to help extend the spine. Its fibers originate on the spinous processes in the lower thoracic and upper lumbar region, typically from L2 to L5. From there, the muscle shortens upward to insert on the spinous processes of the upper thoracic vertebrae. This arrangement lets both sides contract to straighten the spine and maintain posture.

Origin from the spinous processes of the upper thoracic region (T1–T8) would place the start higher than its usual attachment, so that option isn’t correct for the origin. Origins from the cervical area or from transverse processes would point to different muscles or different parts of the spinalis group, not the thoracis portion.