Muscle · Thoracic spine

Longissimus thoracis

Musculus longissimus thoracis

The largest and longest of the three erector spinae columns, and the middle one of the three — it lies between iliocostalis on the outside and spinalis against the spinous processes. It rises from the broad tendon that anchors the whole erector mass to the sacrum and the back of the pelvis, and travels up to catch every thoracic transverse process and the lower nine or ten ribs on its way. Because it spans from pelvis to rib cage without interruption, it is the muscle that pays out under control as you fold forward and hauls you back up again, and it is most of the ridge you feel either side of the spine in the low and mid back.