Intermediate layer of deepest (transversospinales) muscles of back; origin, from the sacrum, sacroiliac ligament, mammillary processes of the lumbar vertebrae, transverse processes of thoracic vertebrae, and articular processes of last four cervical vertebrae; insertion, into the spinous processes of all the vertebrae up to and including the axis; action, rotates vertebral column; nerve supply, dorsal primary rami of spinal nerves. Syn: musculus multifidus spinae, musculus multifidus TA.