Psoas major anatomy: The psoas major is a deep muscle that originates from the transverse processes, vertebral bodies, and intervertebral discs of T12 to L5. It travels downward through the pelvic cavity, passes deep to the inguinal ligament, and inserts into the lesser trochanter of the femur. Along its course, it lies adjacent to the lumbar plexus, ureter, and abdominal aorta. It’s innervated by branches of the lumbar plexus, primarily from spinal nerves L1 to L3, and occasionally L4. Function

Innervation of the Psoas Major The psoas major muscle is innervated by the anterior rami of the lumbar spinal nerves L1, L2, and L3. Nerve Supply • Source: • The anterior rami of L1, L2, and L3 lumbar spinal nerves arise from the lumbar plexus, which is embedded within the psoas major muscle itself. • Pathway: • The anterior rami emerge from the intervertebral foramina and travel through the psoas major muscle. • Branches provide motor innervation to the psoas major. Functional Contribution • Pr