Spinalis Thoracis

Description

Centered along the posterior thoracic spine, the spinalis thoracis appears as paired, dense longitudinal columns immediately adjacent to the thoracic spinous processes, forming the medial component of the erector spinae. Inferior fibers arise from lower thoracic and upper lumbar spinous processes, then course superiorly to insert onto the spinous processes of upper thoracic vertebrae, staying medial to the longissimus thoracis and iliocostalis thoracis. Laterally, the scapulae frame the upper back, with posterior ribs curving outward from the vertebral column and the proximal humeri partially visible at the shoulder girdle. The occipital bone is seen superiorly as the skull base in posterior aspect. Posterior visualization matters because spinalis thoracis is often the least distinct erector spinae subdivision in surface anatomy, yet it directly influences thoracic extension and segmental stabilization through its short, spinous process to spinous process attachments. This relationship becomes clinically relevant when interpreting paraspinal muscle atrophy or asymmetry on MRI in chronic low back pain, and when planning posterior midline approaches to the thoracic spine where subperiosteal dissection along spinous processes can split or denervate medial paraspinal fibers. Small muscle, big consequence. The proximity to the thoracic spinous processes also makes it a clear landmark for teaching how the erector spinae masses flank the midline and how posterior bony elements guide safe dissection planes. Use this artwork in gross anatomy labs, kinesiology modules on trunk extension, or as a figure for spine surgery and musculoskeletal radiology teaching files that need clean orientation of scapulae, ribs, and vertebrae with the spinalis thoracis emphasized. It also fits textbook layouts discussing erector spinae compartmental anatomy and posterior thoracic approaches. Anatomical accuracy verified by SciePro's Medical Advisory Board.