Longissimus Thoracis
Back
The longest erector spinae column in the thorax — one of the main 'anti-slouching' muscles doing quiet background work every time you sit tall or stand upright.
Function
Extends and laterally flexes thoracic/lumbar spine
Origin
Sacrum, iliac crest, lumbar spinous/transverse processes
Insertion
Transverse processes of thoracic vertebrae and ribs
Innervation
Posterior rami of spinal nerves