The longissimus is a deep muscle of the back that participates in the formation of the erector spinae muscle complex along with the iliocostalis and spinalis muscles. The longissimus is the most central of the erector spinae muscles. It is also the longest and thickest of the three.

Based on the location and superior attachments, the longissimus can be subdivided into three parts: longissimus capitis, longissimus cervicis and longissimus thoracis.

Longissimus capitis

The longissimus capitis is the most cranially located longissimus muscle. It stretches between the cervical and thoracic vertebrae and the temporal bone. The longissimus capitis lies medial to the longissimus cervicis.

Origin: transverse processes of the lower three or four cervical (C4/C5 - C7) and upper five thoracic vertebrae (T1 - T5).

Insertion: mastoid process of the temporal bone.

Action: bilateral contractions - extension of the head and neck; unilateral contractions - lateral flexion and rotation of the head to the same side (ipsilateral).

Innervation: lateral branches of the dorsal rami of the cervical spinal nerves.

Blood supply: muscular branches of the occipital, vertebral, deep cervical and transverse cervical arteries.

Longissimus cervicis

The longissimus cervicis is the middle portion of the longissimus muscle complex. It lies medial to the longissimus thoracis, stretching between the thoracic and cervical vertebrae.

Origin: transverse processes of the upper four to five thoracic vertebrae (T1 - T4/T5).

Insertion: posterior tubercles of the transverse processes of the second to sixth cervical vertebrae (C2 - C6).

Action: bilateral contractions - extension of the cervical and thoracic spine; unilateral contractions - lateral flexion of the cervical and thoracic spine to the same side (ipsilateral).

Innervation: lateral branches of the dorsal rami of the cervical spinal nerves.

Blood supply: muscular branches of the occipital, vertebral, deep cervical and transverse cervical arteries.

Longissimus thoracis

The longissimus thoracis is the most caudally located muscle of the longissimus group. It is composed of two parts - thoracic and lumbar.

Origin: thoracic part - spinous and transverse processes of all lumbar vertebrae (L1 - L5), median sacral crest, dorsal surface of the sacrum and posterior aspect of the iliac crest of the ilium; lumbar part - lumbar intermuscular aponeurosis, anteromedial aspect of the sacropelvic surface of the ilium and posterior sacroiliac ligament.

Insertion: thoracic part - transverse processes of all thoracic vertebrae (T1 - T12), angles of ribs 7 to 12; lumbar part - accessory and transverse processes of all lumbar vertebrae (L1 - L5).

Action: bilateral contractions - extension of the thoracic and lumbar spine; unilateral contractions - lateral flexion of the thoracic and lumbar spine to the same side (ipsilateral).

Innervation: lateral and medial branches of the dorsal rami of the thoracic and lumbar spinal nerves.

Blood supply: branches of the superior and posterior intercostal arteries, lateral sacral and median sacral arteries.

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Longissimus muscle