Semispinalis Thoracis, Posterior View

Description

Centered along the posterior thoracic spine, the semispinalis thoracis appears as a deep transversospinalis muscle running superomedially from the transverse processes of the upper thoracic vertebrae to the spinous processes several levels above. Superficial to it lie the broader sheets of trapezius and latissimus dorsi, while the rhomboid minor and rhomboid major span from the thoracic spinous processes to the medial border of the scapula, medial to the infraspinatus fossa. Laterally, the deltoid caps the shoulder, and the scapulae frame the midline, with rib contours suggested beneath the muscular layers. Semispinalis thoracis is easy to ignore until you teach or operate in layers, because it sits deep to the erector spinae group and becomes a key landmark when distinguishing transversospinalis fibers from the longissimus and spinalis columns in the upper back. Its fiber direction and segment-spanning attachments explain why extension and contralateral rotation can reproduce pain in thoracic facet joint irritation and paraspinal strain, and why targeted palpation or trigger point injection requires clear mental mapping of what is superficial (trapezius, rhomboids) versus deep (semispinalis). Small muscle. Big implications for localization. Use this posterior female upper back rendering for gross anatomy lab handouts on intrinsic back muscles, for spine biomechanics lectures that contrast erector spinae with transversospinalis function, or for surgical education modules describing posterior midline approaches and layered dissection to the thoracic laminae. It also supports clinical anatomy content on thoracic back pain patterns and paraspinal compartment anatomy. Anatomical accuracy verified by SciePro's Medical Advisory Board.