Intermediate Deep Layer

• Erector Spinae (3 muscle group)
  • Bony Attachments:
    • 1. Posterior sacrum, iliac crest, sacrotuberous lig., dorsal sacroiliac ligament, Spinous Process of T11-L5, and supraspinous ligament
  • Arterial Supply: Post. br. of internal thoracic a.
  • Iliocostalis (Lateral erector spinae)
    • Bony Attachments:
      • 1. Common origin: ilium, sacrum, Lumber vert., dorsal SI lig.
        • Lumborum
          • 2. Angles of lower 6-12 ribs
        • Thoracis
          • 2. Angles of ribs 1-6, Trans. Proc. C7
        • Cervicis
          • 2. Trans. processes of C4-C6
    • Innervation: Posterior rami of spinal nerves
    • Action: Extend and laterally bend vertebral column
  • Longissimus (Middle part of erector spinae)
    • Thoracis
      • 1. Common origin of erector spinae, Transverse Process (TP) L1-L5
      • 2. TP of T1-T12 and angles of lower 9-10 ribs
      • Innervation: Post. rami of spinal nerves
    • Cervicis
      • 1. TP T1-T5
      • 2. TP of C2-C6
      • Innervation: Post. rami of spina nerves C3-C4
      • Action: Extend and laterally bend vertebral column
    • Capitis
      • 1. TP T1-T5 and articular processes of C4-C7
      • 2. TP several levels above & Mastoid process of temporal bone
      • Innervation: Post. rami of spinal nerves C3-C4
      • Action: Extend head
  • Spinalis (most medial part of erector spinae)
    • Thoracis
      • 1. Spinous process (SP) of T11-L2
      • 2. SP T1-T4
      • Innervation: Post. rami of spinal nerves
      • Action: Extend vertebral column
    • Cervicis
      • 1. Inferior part of nuchal ligament, SP C7-T2
      • 2. SP T1-T4
      • Innervation: Post. rami of spinal nerves
      • Action: Extend head
    • Capitis
      • 1. TP of C7-T6
      • 2. Occiput between superior and inferior nuchal lines
      • Innervation: Post. rami of spinal nerves
      • Action: Extend head