Muscle · Thoracic spine

Spinalis thoracis

Musculus spinalis thoracis

The smallest and most medial of the three erector spinae columns, lying directly against the spinous processes and joining the lower thoracic and upper lumbar spines to the upper thoracic ones. It is thin, often incompletely separate from longissimus beside it, and it blends so intimately with that column that in most bodies it cannot be dissected out cleanly, let alone felt through skin. What it adds is a short, near-vertical line of pull very close to the spine — extension applied right at the segments rather than across them.