The small psoas muscle is one of the muscles that form the posterior abdominal wall. It is found in about 50% of subjects. It originates from the lateral faces of the twelfth thoracic vertebra and the first lumbar vertebra as well as from the respective intervertebral discs. It is part of the ileopubic eminence and iliac fascia. It is a weak flexor of the trunk and with its action the iliac fascia extends. It is innervated by a direct branch of the L1-L3 lumbar plexus.
| ORIGIN Lateral faces of the bodies of T12 and L1 and respective vertebral discs |  |
| INSERTION Ileopubic eminence and iliac fascia | |
| ACTION Weak flexor of the trunk, contracting the iliac fascia tends | |
| INNERVATION Direct branch of the L1-L3 lumbar plexus |
| Upper limb | Lower limb | Trunk | Abdomen | Articles |
