Psoas major

Origin

The psoas major is a long, thick, fusiform muscle situated on the posterior abdominal wall, immediately lateral to the vertebral column. It arises from the bodies, intervertebral discs, and transverse processes of the T12–L5 vertebrae.

Course and insertion

The psoas major muscle descends across the brim of the lesser pelvis, gradually tapering as it passes beneath the inguinal ligament and in front of the hip-joint capsule before terminating in a tendon. This tendon receives fibres from the Iliacus and inserts onto the lesser trochanter of the femur as part of the common iliopsoas tendon. A large bursa, which may communicate with the hip-joint cavity, separates the tendon from the pubis and the joint capsule.

Functional note

Together, the psoas major and iliacus act together as the iliopsoas, serving as the chief flexor of the hip — essential for walking, running, and maintaining upright posture.