Semispinalis Thoracis, Posterior View

Description

Deep to the superficial back layers, the semispinalis thoracis lies on the posterior thoracic spine as a vertically oriented member of the transversospinalis group. Its muscle bellies arise from the transverse processes of the upper thoracic vertebrae and run superomedially to insert on the spinous processes several segments above, placing it medial to the rib angles and immediately posterior to the vertebral laminae. In a posterior dissection context, it sits deep to spinalis and longissimus thoracis and is typically covered by semispinalis capitis and cervicis superiorly as the fibers continue toward the lower cervical region. Segmental innervation from the posterior (dorsal) rami tracks along the deep surface. This posterior perspective matters when you need to distinguish intrinsic stabilizers of the thorax from the scapulothoracic muscles that dominate more superficial views. Semispinalis thoracis is a key driver of thoracic extension and contralateral rotation, and it becomes clinically relevant in midline posterior approaches where the paraspinal muscles are stripped from the spinous processes, as well as in thoracic medial branch blocks and radiofrequency ablation targeting the dorsal rami that course through these deep planes. Deep back pain often localizes here. Clear fiber direction makes level counting and “skip” insertions easier to teach. Use this asset in gross anatomy lab manuals, musculoskeletal and spine modules, and surgical education materials covering posterior thoracic exposure, paraspinal compartment anatomy, or the transversospinalis group in relation to dorsal rami interventions. It also fits well in atlases and exam prep resources that contrast intrinsic back musculature with extrinsic scapular retractors such as rhomboid major, which can be shown superficially in companion plates. Anatomical accuracy verified by SciePro's Medical Advisory Board.