erector spinae (muscles)

e·rec·tor spi·nae (mus·cles)

[TA]
proper muscles of back; origin, from sacrum, ilium, and spines of lumbar vertebrae; it divides into three columns, iliocostalis musculus, longissimus musculus, and spinalis musculus, which insert into ribs and vertebrae with additional muscle slips joining the columns at successively higher levels; action, extends and laterally flexes vertebral column; nerve supply, dorsal primary rami of spinal nerves.