Back muscles: the superficial, intermediate and deep muscles of the back

The muscles of the back are divided into three groups: superficial, intermediate and deep. The deep muscles develop in the back itself, so they are called intrinsic (or true) back muscles. The superficial and intermediate muscles develop elsewhere and migrate onto the back, so they are called extrinsic back muscles. (TeachMeAnatomy: The Superficial Back Muscles.)

Each layer has a different job. The superficial muscles are associated with movements of the shoulder and upper limb. The intermediate muscles connect the vertebral column to the rib cage and move the ribs. The deep muscles act on the vertebral column, keeping it upright, bending and twisting it, and controlling posture. (TeachMeAnatomy: The Intermediate Back Muscles.)

The intrinsic muscles are themselves arranged in layers. From superficial to deep they are the spinotransversales (splenius capitis and splenius cervicis), the erector spinae (iliocostalis, longissimus and spinalis), the transversospinales (semispinalis, multifidus and rotatores) and a set of small segmental muscles. They are covered by deep fascia, which helps to organise them. (TeachMeAnatomy: The Intrinsic Back Muscles.)

Trapezius is the large, flat, most superficial muscle of the upper back and neck. It arises from the skull, the ligamentum nuchae (the midline ligament of the back of the neck) and the spinous processes of C7 to T12, and inserts on the clavicle, the acromion and the spine of the scapula. Its upper fibres elevate the scapula and help rotate it during abduction of the arm, its middle fibres retract (pull back) the scapula and its lower fibres pull the scapula down. (TeachMeAnatomy: The Superficial Back Muscles.)

Trapezius gets its motor supply from the accessory nerve (cranial nerve XI); fibres from C3 and C4 carry proprioception. The most common cause of accessory nerve injury is iatrogenic, for example during a cervical lymph node biopsy. The nerve is tested by asking the patient to shrug their shoulders. (TeachMeAnatomy: The Superficial Back Muscles.)

Latissimus dorsi is the broad, flat muscle of the lower back. It arises from the spinous processes of the inferior six thoracic vertebrae, the thoracolumbar fascia, the iliac crest and the inferior three or four ribs, and inserts into the floor of the intertubercular groove of the humerus. It extends, adducts and medially rotates the humerus and raises the body towards the arms when climbing. It is supplied by the thoracodorsal nerve (C6, C7 and C8) and the thoracodorsal artery. (University of Washington Musculoskeletal Atlas: Latissimus dorsi.)

Levator scapulae arises from the transverse processes of C1 to C4 and attaches to the medial border of the scapula; it elevates the scapula. Rhomboid minor runs from the spinous processes of C7 and T1 to the medial border of the scapula at the level of the scapular spine. Rhomboid major, just below it, runs from the spinous processes of T2 to T5 to the medial border between the spine and the inferior angle. Both rhomboids retract and rotate the scapula, and all three muscles are supplied by the dorsal scapular nerve. (TeachMeAnatomy: The Superficial Back Muscles.)

Attachments, nerve supply and the role of levator scapulae in neck stiffness. Levator scapulae.

The intermediate layer has two thin muscles that run from the spine to the ribs. Serratus posterior superior is thin and rectangular and lies deep to the rhomboids. It arises from the lower part of the ligamentum nuchae and the spinous processes of about C7 to T3; its fibres pass downwards and outwards to attach to ribs 2 to 5, which it elevates. (TeachMeAnatomy: The Intermediate Back Muscles.)

Serratus posterior inferior is broader and stronger and lies under latissimus dorsi. It arises from the spinous processes of about T11 to L3; its fibres pass upwards and outwards to ribs 9 to 12, which it depresses. Both muscles are supplied by intercostal nerves and are thought to have only a slight role in breathing. (TeachMeAnatomy: The Intermediate Back Muscles.)

The splenius muscles are the most superficial of the deep back muscles. They begin at the midline and run upwards and outwards (superolaterally) to their insertions. Splenius capitis inserts on the head, and splenius cervicis inserts on the cervical vertebrae. (OpenStax Anatomy and Physiology 2e, 11.3: Axial Muscles of the Head, Neck, and Back.)

Splenius capitis arises from the lower half of the nuchal ligament and the spinous processes of C7 to T3 and inserts on the mastoid process and the occipital bone just below the superior nuchal line. It lies under trapezius and over semispinalis capitis and longissimus capitis. Acting together, the two muscles extend the head; one muscle acting alone turns the head to the same side. (Kenhub: Splenius capitis muscle.)

Splenius cervicis arises from the spinous processes of T3 to T6 and inserts on the transverse processes of C1 to C3. Acting on one side it bends and rotates the neck to the same side, and acting together the two muscles help trapezius to extend the neck. It is supplied by the posterior rami of the lower cervical spinal nerves. (Kenhub: Splenius cervicis muscle.)

Attachments, relations, nerve supply and clinical notes on the splenius capitis. Splenius capitis.

The erector spinae forms most of the muscle mass of the back. It is made of three columns side by side: iliocostalis on the outside (laterally), longissimus in the middle and spinalis next to the spinous processes (medially). Each column has parts named after the region where it ends, such as iliocostalis cervicis, longissimus capitis and spinalis capitis. (OpenStax Anatomy and Physiology 2e, 11.3: Axial Muscles of the Head, Neck, and Back.)

The three columns share a common tendinous origin from the lower thoracic and lumbar vertebrae, the sacrum, the back of the iliac crest, and the sacroiliac and supraspinous ligaments. Iliocostalis (which has lumborum, thoracis and cervicis parts) inserts into the angles of the ribs and the cervical transverse processes. Longissimus inserts into the lower ribs, the transverse processes of C2 to T12 and the mastoid process. Spinalis inserts into the spinous processes of C2 and T1 to T8 and into the occipital bone. (TeachMeAnatomy: The Intrinsic Back Muscles.)

All three columns have the same actions. When the muscles on one side contract, they bend the vertebral column to that side (lateral flexion). When both sides contract together, they extend the vertebral column and the head, straightening the back from a bent position. All are supplied by the posterior rami of the spinal nerves. (TeachMeAnatomy: The Intrinsic Back Muscles.)

The transversospinales run from the transverse processes of the vertebrae up and in towards the spinous processes, filling the groove between the two. The semispinalis group (semispinalis capitis, cervicis and thoracis) is the most superficial of them. (OpenStax Anatomy and Physiology 2e, 11.3: Axial Muscles of the Head, Neck, and Back.)

Semispinalis arises from the transverse processes of C4 to T10 and climbs four to six segments to the spinous processes of C2 to T4 and to the occipital bone. It extends the head and vertebral column and turns them to the opposite side. Multifidus lies deeper and spans two to four segments. Rotatores are the deepest of all: each runs from a transverse process to the lamina and spinous process of the vertebra above. Rotatores help extension and rotation, stabilise the vertebrae and are thought to have a proprioceptive role, sensing the position of the spine. (TeachMeAnatomy: The Intrinsic Back Muscles.)

Under the transversospinales lie small segmental muscles that join neighbouring vertebrae. Interspinales span adjacent spinous processes and intertransversarii span adjacent transverse processes; both stabilise the vertebral column. Levatores costarum arise from the transverse processes of C7 to T11 and attach to the rib just below, which they elevate. (TeachMeAnatomy: The Intrinsic Back Muscles.)

Multifidus is a transversospinal muscle with a very broad origin: the sacrum, the posterior superior iliac spine, the tendon of erector spinae, the mamillary processes of the lumbar vertebrae, the transverse processes of T1 to T3 and the articular processes of C4 to C7. Its fibres climb two to four segments to the spinous processes above. It is most developed in the lumbar area and its main role is to stabilise the vertebral column. The BodyParts3D model used on this site does not include multifidus. (TeachMeAnatomy: The Intrinsic Back Muscles.)

In the lumbar region multifidus fills the groove on each side of the spinous processes and has the largest attachment area of the paravertebral muscles. It is described as the only lumbar paraspinal muscle supplied by a single nerve root, and as the main muscle that maintains lumbar stability. Most patients with lumbar degenerative disease show atrophy (shrinkage) and fat infiltration of multifidus. (Wang X et al. Research Progress on the Mechanism of Lumbar Multifidus Injury and Degeneration. Oxid Med Cell Longev. 2021.)

Textbooks do not all agree on where multifidus sits. A 2020 scoping review found that anatomy atlases mostly draw lumbar multifidus as a deep muscle covered by the erector spinae and the thoracolumbar fascia, while research papers describe it as superficial, deep or both. The authors concluded that descriptions are not standardised and that atlases should be updated. (Hofste A et al. Inconsistent descriptions of lumbar multifidus morphology: a scoping review. BMC Musculoskelet Disord. 2020.)

The thoracolumbar fascia (Latin fascia thoracolumbalis) is a sheet of dense connective tissue in the lower back that separates the paraspinal muscles from the posterior abdominal wall. Its posterior layer has a superficial lamina made mostly of the aponeuroses (flat tendons) of latissimus dorsi and serratus posterior inferior, and a deeper lamina that wraps the paraspinal muscles in a sheath. (Willard FH et al. The thoracolumbar fascia: anatomy, function and clinical considerations. J Anat. 2012.)

Along the outer edge of this sheath, a seam called the lateral raphe forms where it meets the aponeuroses of transversus abdominis and internal oblique. This links the back muscles to the abdominal wall as one girdle that helps with posture, load transfer and breathing. Authors describe the fascia with either a two-layer or a three-layer model; the three-layer model is used in most research. (Willard FH et al. The thoracolumbar fascia: anatomy, function and clinical considerations. J Anat. 2012.)

The model is built from the BodyParts3D data set (adult male). It shows the three parts of trapezius (descending, transverse and ascending), levator scapulae, both rhomboids, both serratus posterior muscles, the splenius muscles, the parts of the erector spinae, semispinalis, rotatores, interspinales and levatores costarum. It does not contain latissimus dorsi or multifidus, which are described above. To find the erector spinae, look on either side of the spinous processes in the lumbar region, where they are not covered by other muscles in the model.

When you name back muscles on a labelled diagram, work in layers. Trapezius and latissimus dorsi are on the surface; the rhomboids and levator scapulae lie under trapezius; serratus posterior lies under these; then come splenius, the erector spinae columns, the transversospinales and finally the small segmental muscles next to the bones. (TeachMeAnatomy: The Intrinsic Back Muscles.)

Ascending part of trapezius

The lower fibres of trapezius, running upward and laterally to the scapular spine.

Cervical rotator

Small deep muscles of the neck's transversospinalis group (rotatores cervicis).

Descending part of trapezius

The upper fibres of trapezius, running down from the skull and neck.

Iliocostalis cervicis

The cervical part of the iliocostalis column of erector spinae.

Iliocostalis lumborum

The lumbar part of the iliocostalis column of erector spinae.

Iliocostalis thoracis

The thoracic part of the iliocostalis column of erector spinae.

Interspinalis thoracis

A tiny muscle between adjacent thoracic spinous processes, often poorly developed.

Levator scapulae

A muscle of the posterolateral neck that raises the scapula.

Longissimus capitis

The part of longissimus attaching to the skull.

Longissimus cervicis

The cervical part of the longissimus column.

Longissimus thoracis

The largest part of the longissimus column of erector spinae.

Lumbar rotator

Small deep muscles of the transversospinalis group in the lumbar spine (rotatores lumborum).

Rhomboid major

A flat muscle deep to trapezius that connects the spine to the scapula.

Rhomboid minor

A small muscle lying above rhomboid major.

Semispinalis capitis

A large muscle of the posterior neck forming the bulge beside the midline.

Semispinalis cervicis

A transversospinal muscle of the neck deep to semispinalis capitis.

Semispinalis thoracis

A transversospinal muscle of the upper back.

Serratus posterior inferior

A thin muscle of the lower back deep to latissimus dorsi.

Serratus posterior superior

A thin muscle of the upper back deep to the rhomboids.

Interspinales cervicis

Short paired muscles between the spinous processes of adjacent cervical vertebrae.

Interspinales lumborum

Short paired muscles between the spinous processes of adjacent lumbar vertebrae.

Levatores costarum breves

Short triangular muscles on the back of the thorax, part of the twelve pairs of levatores costarum.

Levatores costarum longi

Longer slips of the levatores costarum on the lower thoracic back.

Spinalis

The most medial column of the erector spinae group, lying beside the spinous processes.

Spinalis thoracis

The thoracic part of spinalis, the medial column of the erector spinae.

Splenius capitis

A flat bandage-like muscle on the back of the neck.

Splenius cervicis

A strap-like muscle deep to splenius capitis.

Thoracic rotator

Small muscles deep in the groove between the spinous and transverse processes of thoracic vertebrae, called rotatores thoracis.

Transverse part of trapezius

The middle fibers of trapezius, running horizontally.