[TA] deepest of the three layers of transversospinalis muscles, chiefly developed in the thoracic region; they arise from the transverse process of one vertebra and are inserted into the root of the spinous process of the next two or three vertebrae above; action, traditionally described as a column, it is more likely that these muscles, provided with a very high density of muscle spindles, are organs of proprioception; nerve supply, dorsal primary rami of the spinal nerves. SYN: musculi rotatores [TA].