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Longissimus

The longissimus (Latin: musculus longissimus) is a deep muscle of the back that forms the erector spinae along with both iliocostalis and spinalis muscles. The longissimus is the most central erector spinae muscle. It is also the longest and thickest of the three. The longissimus is divided into three parts based on location and superior attachment: longissimus capitis, longissimus cervicis, and longissimus thoracis.

 

Longissimus capitis

The longissimus capitis (also known as trachelomastoid muscle, Latin: musculus longissimus capitis) is a portion of the longissimus muscle in the neck region that lies medial to the longissimus cervicis.

Origin

The longissimus capitis originates by tendons arising from the transverse processes of the lower three or four cervical vertebrae (C4/C5 - C7) and upper four thoracic vertebrae (T1 - T4).

Insertion

The fibers of the longissimus capitis insert into the posterior edge of the mastoid process of the temporal bone.

Action

This muscle has very little force capacity. Bilateral activation of the longissimus capitis may aid in extending the head and neck. Unilateral activation laterally flexes and rotates the head ipsilaterally (to the same side).

Innervation

The longissimus capitis is innervated by the lateral branches of the dorsal rami of cervical and thoracic spinal nerves (C6 - T4).

Blood supply

The blood supply to the longissimus capitis and cervicis is provided by the muscular branches of the occipital artery, which itself arises from the external carotid artery, as well as by the vertebral arterydeep cervical artery, and transverse cervical artery.

 

Longissimus cervicis

The longissimus cervicis (also known as transversalis cervicis, Latin: musculus longissimus cervicis; musculus longissimus colli) is a portion of the longissimus muscle that lies medial to the longissimus thoracis.

Origin

The longissimus cervicis originates by tendons from the transverse processes of the upper four or five thoracic vertebrae (T1 - T4/T5).

Insertion

The fibers of the longissimus cervicis insert into the posterior tubercles of transverse processes of the second to sixth cervical vertebrae (C2 - C6).

Action

When acting bilaterally, the longissimus cervicis extends the cervical spine while unilaterally laterally flexes the cervical spine ipsilaterally (to the same side). However, this muscle has very little force capacity.

Innervation

The longissimus cervicis is innervated by the lateral branches of the dorsal rami of the thoracic spinal nerves.

Blood supply

The blood supply to the longissimus capitis and cervicis is provided by the muscular branches of the occipital artery, which itself arises from the external carotid artery, as well as by the vertebral artery, deep cervical artery, and transverse cervical artery.

 

Longissimus thoracis

The longissimus thoracis (Latin: musculus longissimus thoracis) is the lower portion of the longissimus muscle. It is divided into two parts: the lumbar part and the thoracic part. 

Origin

The lumbar part of the longissimus thoracis originates from the lumbar intermuscular aponeurosis, the anteromedial aspect of the ilium, and the posterior sacroiliac ligament.

The thoracic part arises from the spinous and transverse processes of the first to fifth lumbar vertebrae (L1 - L5), the medial sacral crest, posterior surface of the sacrum and the posterior iliac crest.

Insertion

The muscle fibers of the lumbar part insert into the accessory and transverse processes of the first to fifth lumbar vertebrae (L1 - L5). 

The thoracic part of the longissimus inserts into the transverse processes of the twelve thoracic vertebrae (T1 - T12) and the angles of ribs 7 to 12.

Action

Upon bilateral contraction, the longissimus thoracis like other parts of the longissimus muscle extends the spine, and upon bilateral contraction, it laterally flexes the spine to the same side.

Innervation

The longissimus thoracis is innervated by the lateral branches of the dorsal (posterior) rami of the thoracic and lumbar spinal nerves (T7 - L5).

Blood supply

The longissimus thoracis is supplied by the dorsal branches of the posterior intercostal arteries and the subcostal arteries arising from the thoracic aorta, as well as by the lateral sacral and median sacral arteries.