The longissimus is a deep muscle of the back. It is situated between the iliocostalis and spinalis within the erector spinae complex, and can be divided into three separate parts. These three parts are: the thoracic, cervicis, and capitis.
The longissimus muscle arises from the lower thoracic and lumbar vertebrae, the sacrum, and the posterior aspect of the iliac crest. It then attaches to the lower ribs, the transverse processes of C2-T12, and the mastoid process of the skull.
The longissimus muscle is responsible for two actions. Firstly, when acted upon unilaterally, it can laterally flex the vertebral column. Secondly, when acted upon bilaterally, it can extend the vertebral column and head.
The longissimus muscle is innervated by the posterior rami of the spinal nerves. In terms of its blood supply, the longissimus thoracic muscle receives blood supply from the dorsal branches of the posterior intercostal and sacral arteries. On the other hand, the longissimus cervicis and capitis muscles are supplied with blood from the transverse cervical, occipital, vertebral, and deep cervical arteries.
