MRI scans with neck muscles outlined. Axial proton density-weighted MRI images at C2 (left) and C5 (right) of a subject in the neutral posture. Neck muscles are outlined and identified by number: 1—Sternocleidomastoid, 2—Trapezius, 3—Splenius Capitis, 4—Splenius Cervicis, 5—Semispinalis Capitis, 6—Semispinalis Cervicis+Multifidus (traced together), 7—Longissimus Capitis, 8—Longissimus Cervicis, 9—Levator Scapulae, 10—Longus Capitis, 11—Longus Colli, 12—Obliqus Capitis Inferior, 13—Rectus Capitis Posterior Major, 14—Scalenus Anterior, 15—Scalenus Posterior, 16—Infrahyoids.