The spinalis is one of the muscles forming the erector spinae - a muscle group of the deep back muscles, the other two being the longissimus and iliocostalis. The spinalis is the most medial of the three. This muscle is formed from three parts: spinalis capitis, cervicis, and thoracis.

The spinalis mainly originates from and inserts into spinous processes of the cervical and thoracic vertebrae, but also its capitis part attaches to the skull. This muscle provides extension and lateral flexion of the cervical and thoracic parts of the spine.

The spinalis is innervated by the lateral branches of the dorsal rami of the spinal nerves.

The blood supply is provided mainly by the dorsal branches of the posterior intercostal arteries, the deep cervical artery, and the muscular branches of the vertebral artery.

Spinalis capitis

Origin: spinous processes of the C7 to T1 vertebrae.
Insertion: occipital bone, near its midline.
Action: upon bilateral contraction - extends the head and neck, while upon unilateral contraction - provides lateral flexion of the cervical spine to the same side (ipsilaterally).

Spinalis cervicis

Origin: spinous processes of the C7 to T1 vertebrae, and the nuchal ligament.
Insertion: spinous processes of the C2 to C4 vertebrae.
Action: upon bilateral contraction - extends the cervical spine, while upon unilateral contraction - provides lateral flexion of the cervical spine to the same side (ipsilaterally).

Spinalis thoracis

Origin: spinous processes of the T11 - L2 vertebrae.
Insertion: spinous processes of the T2 to T8 vertebrae.
Action: a bilateral contraction - provides extension of the thoracic spine, while an unilateral contraction - lateral flexion of the thoracic spine to the same side (ipsilaterally).

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Spinalis muscle