02/04/2026
What you’re looking at here is the deep posterior abdominal wall and lower thoracic region, with the superficial layers removed so you can actually see how these structures relate in real human tissue rather than a clean textbook diagram.
At the very top, running along the inferior border of the 12th rib, is the subcostal muscle. This is essentially the continuation of the innermost intercostal layer once you run out of intercostal spaces. It sits deep, close to the pleura, and its role is minor in respiration, more about fine control of the lower rib rather than producing forceful movement.
Deep to that, and spanning from the iliac crest up to the 12th rib and transverse processes of the lumbar spine, is quadratus lumborum. In cadaveric tissue like this, it often looks flatter and broader than people expect. Clinically, it’s a frequent contributor to deep lumbar and flank pain, not because it’s “tight” or “short,” but because it’s heavily involved in load transfer and sustained postural tasks.
Medial to QL you can see psoas major, running vertically along the lumbar vertebral bodies. In real anatomy it’s much more substantial and irregular than the neat fusiform muscle shown in models. Its intimate relationship with the lumbar discs, vertebral bodies, and neural structures is obvious here, which explains why lumbar spine issues and deep anterior hip pain often coexist.
You can also see iliacus inferiorly, lining the inner surface of the ilium and blending with psoas to form the iliopsoas complex. Again, this highlights that these muscles are not isolated structures but part of a continuous regional system.
What these images do well is strip away the myths. There’s no obvious “knot,” nothing visibly “out of place,” and no single structure that can be blamed in isolation. Pain in this region is rarely about one muscle misbehaving and far more about how these tissues are interacting with load, movement, and the nervous system over time.
