Longissimus thoracis muscle

Origin:

• Lumbar part - Lumbar intermuscular aponeurosis, medial part of sacropelvic surface of ilium, Posterior sacroiliac ligament

• Thoracic part - Spinous and transverse processes of vertebrae L1-L5,  median sacral crest, posterior surface of sacrum and posterior iliac crest

Insertion:

• Lumbar part - Accessory and transverse processes of vertebrae L1-L5

• Thoracic part - Transverse process of vertebrae T1-T12, Angles of ribs 7-12

Artery: superior intercostal, posterior intercostal and subcostal arteries; lateral sacral and median sacral arterie

Nerve: Posterior branch of spinal nerve

Antagonist: Rectus abdominis muscle

Description: The Longissimus thoracis muscle (Longissimus dorsi) is the intermediate and largest of the continuations of the part of the erector spinae muscle group.

In the thoracic region the Longissimus thoracis muscle is inserted, by rounded tendons, into the tips of the transverse processes of all the thoracic vertebrae, and by fleshy processes into the lower nine or ten ribs between their tubercles and angles.

In the lumbar region, where it is as yet blended with the Iliocostalis lumborum, some of its fibers are attached to the whole length of the posterior surfaces of the transverse processes and the accessory processes of the lumbar vertebrae, and to the anterior layer of the lumbodorsal fascia. This part of the muscle is called Lumbar part of longissimus thoracis muscle (previously called Longissimus lumborum,).

These two parts of the Longissimus thoracis are sometimes referred to as the Longissimus thoracis et lumborum (LTL).