spinalis thoracis

noun

spinalis tho·​ra·​cis -thə-ˈrā-səs 

: an upward continuation of the sacrospinalis that is situated medially to and blends with the longissimus thoracis, arises from the spinous processes of the first two lumbar and last two thoracic vertebrae, and inserts into the spinous processes of the upper thoracic vertebrae