The deep or intrinsic muscles of the back extend from the pelvis to the skull and are innervated by segmental branches of the posterior rami of spinal nerves. They include: the extensors and rotators of the head and neck— the splenius capitis and cervicis (spinotransversales muscles), the extensors and rotators of the vertebral column—the erector spinae and transversospinales, and the short segmental muscles—the interspinales and intertransversarii.