Longissimus thoracis muscle

Musculus longissimus thoracis

Longissimus thoracis is the large middle column of erector spinae in the back, running from the sacrum to the thoracic vertebrae and ribs.

At a glance

English: Longissimus thoracis muscle
Latin (TA2): Musculus longissimus thoracis
System: Muscle
Region: Back
Side: Paired, left and right
Inserts on: The eighth rib, eleventh rib, fifth rib, first rib, fourth rib, ninth rib, second rib, seventh rib, sixth rib, tenth rib, third rib, twelfth rib, vertebra l1, vertebra l2, vertebra t1, vertebra t10, vertebra t11, vertebra t12, vertebra t2, vertebra t3, vertebra t4, vertebra t5, vertebra t6, vertebra t7, vertebra t8 and vertebra t9

About the longissimus thoracis muscle

Longissimus is Latin for the longest, and it is the middle of the three columns of erector spinae, lying between iliocostalis outside and spinalis inside. It is also the largest. The thoracic section, longissimus thoracis, runs the length of the lower and middle back and is continued into the neck and head by longissimus cervicis and longissimus capitis.

Its fibres arise from the common erector spinae tendon on the sacrum, iliac crest and lumbar spines. In the lower back the muscle is still merged with iliocostalis and attaches to the backs of the lumbar transverse and accessory processes and to the thoracolumbar fascia. Higher up it gives two rows of insertions: rounded tendons on the transverse process tips of every thoracic vertebra, and fleshy slips on most ribs from about the third or fourth down to the twelfth, between tubercle and angle.

Acting on both sides, the muscle is a powerful extensor of the thoracic and lumbar spine. It straightens the back from a bent position, holds the trunk upright and controls bending forward. Acting on one side, it bends the trunk to that side. Its pull on the ribs is small and mainly helps to fix them.

The muscle is supplied by lateral branches of the dorsal rami of the thoracic and lumbar spinal nerves, and blood comes from the posterior intercostal, subcostal and lumbar arteries. It is one of the muscles most often involved in back strain and spasm, and it forms the prominent ridges either side of the midline in the lower back.

Attachments, action and supply

Origin: Common erector spinae tendon from the sacrum, iliac crest and lumbar spines; lumbar transverse and accessory processes.
Insertion: Transverse process tips of all thoracic vertebrae, and ribs from about the third or fourth to the twelfth between tubercle and angle.
Action: Extends the thoracic and lumbar spine on both sides; bends it to the same side on one side.
Nerve supply: Lateral branches of the dorsal rami of the thoracic and lumbar spinal nerves.
Blood supply: Dorsal branches of the posterior intercostal, subcostal and lumbar arteries.

Parts of the longissimus thoracis muscle

Each number is marked on the model. Press one, here or on the model, to see it named in place.

Insertion on the eighth ribA fleshy slip on rib 8, placed between the tubercle and the angle. Pull here helps to extend the spine and draw the rib down.
Insertion on the eleventh ribOne of the lowest costal slips, on rib 11 between its tubercle and angle. Near the lumbar region it blends with iliocostalis.
Insertion on the fifth ribA fleshy slip on rib 5, placed between the tubercle and the angle. Pull here helps to extend the spine and draw the rib down.
Insertion on the first ribA slip to the back of rib 1, between its tubercle and angle. Most textbooks give the costal slips as starting at about rib 3 or 4, so this slip is small or inconstant.
Insertion on the fourth ribA fleshy slip on rib 4, placed between the tubercle and the angle. Pull here helps to extend the spine and draw the rib down.
Insertion on the ninth ribA fleshy slip on rib 9, placed between the tubercle and the angle. Pull here helps to extend the spine and draw the rib down.
Insertion on the second ribA slip to the back of rib 2, between its tubercle and angle. Most textbooks give the costal slips as starting at about rib 3 or 4, so this slip is small or inconstant.
Insertion on the seventh ribA fleshy slip on rib 7, placed between the tubercle and the angle. Pull here helps to extend the spine and draw the rib down.
Insertion on the sixth ribA fleshy slip on rib 6, placed between the tubercle and the angle. Pull here helps to extend the spine and draw the rib down.
Insertion on the tenth ribA fleshy slip on rib 10, placed between the tubercle and the angle. Pull here helps to extend the spine and draw the rib down.
Insertion on the third ribA fleshy slip on rib 3, placed between the tubercle and the angle. Pull here helps to extend the spine and draw the rib down.
Insertion on the twelfth ribOne of the lowest costal slips, on rib 12 between its tubercle and angle. Near the lumbar region it blends with iliocostalis.
Insertion on the vertebra l1Fibres on the L1 transverse and accessory processes. Here the muscle is still fused with iliocostalis.
Insertion on the vertebra l2Fibres on the L2 transverse and accessory processes, part of the lumbar portion of the muscle.
Insertion on the vertebra t1A rounded tendon on the tip of the T1 transverse process, the highest vertebral slip. Longissimus cervicis begins close by.
Insertion on the vertebra t10A rounded tendon on the tip of the T10 transverse process. These slips extend and steady the thoracic spine.
Insertion on the vertebra t11A rounded tendon on the tip of the T11 transverse process. These slips extend and steady the thoracic spine.
Insertion on the vertebra t12A rounded tendon on the tip of the T12 transverse process, where the thoracic slips give way to lumbar ones.
Insertion on the vertebra t2A rounded tendon on the tip of the T2 transverse process. These slips extend and steady the thoracic spine.
Insertion on the vertebra t3A rounded tendon on the tip of the T3 transverse process. These slips extend and steady the thoracic spine.
Insertion on the vertebra t4A rounded tendon on the tip of the T4 transverse process. These slips extend and steady the thoracic spine.
Insertion on the vertebra t5A rounded tendon on the tip of the T5 transverse process. These slips extend and steady the thoracic spine.
Insertion on the vertebra t6A rounded tendon on the tip of the T6 transverse process. These slips extend and steady the thoracic spine.
Insertion on the vertebra t7A rounded tendon on the tip of the T7 transverse process. These slips extend and steady the thoracic spine.
Insertion on the vertebra t8A rounded tendon on the tip of the T8 transverse process. These slips extend and steady the thoracic spine.
Insertion on the vertebra t9A rounded tendon on the tip of the T9 transverse process. These slips extend and steady the thoracic spine.

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At a glance

About the longissimus thoracis muscle

Attachments, action and supply

Related structures

See the longissimus thoracis muscle where it really sits, with every layer of the body around it.