Longissimus thoracis muscle Origin: Fuses with the iliocostals at lumbar level: sacrum, spinous processes of lumbar vertebrae, supraspinous ligaments and iliac crest. Insertion : Transverse processes of all thoracic vertebrae and costal tubercles of the second-twelfth ribs. Innervation: Posterior branches of spinal nerves. Action: Bilateral contraction: Extension of the spine. Anterior pelvic tilt. Unilateral contraction: Lateral flexion of the spine. #backmuscles #anatomy | Bradley Blair Osteop

The longissimus thoracis is part of the erector spinae muscle group, running along the spine to provide extension, lateral flexion, and stabilisation of the thoracic and lumbar regions. Tension Lines and Fibre Orientation • Vertical Orientation: The muscle fibres run longitudinally, from the transverse processes of the lumbar vertebrae and thoracolumbar fascia, extending upward to the transverse processes of the thoracic vertebrae and adjacent ribs. • Functional Tension Lines: • Extension Forces

The longissimus muscle is a long intrinsic muscle of the back. Along with spinalis and iliocostalis, these three muscles comprise the erector spinae group. The erector spinae is a large musculotendinous complex that runs along the entire length of the vertebral column and comprises the intermediate layer of the intrinsic, or deep, back muscles. Longissimus is the longest, thickest and most central erector spinae muscle. It is divided into three parts (capitis, cervicis, thoracis) based on their