The lumbar plexus is formed lateral towards the intervertebral foramina through the ventral rami of the first 4 lumbar spinal nerves (L1-L4), which all go through psoas main. The larger branches of your plexus exit the muscle to move sharply downward to reach the abdominal wall along with the thigh https://www.sgvascularctr.com/swelling-leg-treatment-singapore/