The lumbar iliocostal muscle (iliocostal lumborus) is the lumbar part of the iliocostal muscle.
It is well distinguishable as and independent muscle in carnivores only, while in the pigs and the horse, it is fused with the lumbar portion of the latissimus dorsi.
In carnivores, it attaches to the ends of the transverse processes of the lumbar vertebrae and inserts with fleshy serrations on the 11th to 13th ribs. In ruminants, the tendon of insertion attaches of the last ribs only. In the horse a very short lumbar portion inserts on the transverse processes on the middle lumbar vertebrae.
Origin: Pelvic surface of the wing of the ilium, iliac crest and intermuscular septum.
Insertion: Tenth through thirteenth ribs.
Action: Fixation of the vertebral column or lateral movement when only one side contracts; aids in expiration by pulling the ribs caudally.
Nerve: Dorsal branches of the thoracic and lumbar nerves