Overview
The epaxial muscles form three parallel columns, from lateral to medial:
- Iliocostalis (m. iliocostalis): from the ilium and lumbar vertebrae to the ribs.
- Longissimus (m. longissimus): the largest, from the ilium to the skull, between the transverse and spinous processes.
- Transversospinalis (m. transversospinalis): short bundles next to the spinous processes (spinalis, semispinalis, multifidus, rotatores).
The model shows the three columns as a single mass, from the sacrum to the axis. Cattle have a well developed nuchal ligament, which passively carries the weight of the head and relieves the dorsal neck muscles.
In meat science, the longissimus thoracis et lumborum (the "longissimus dorsi") is the most valuable cut of the carcass: it forms the rib eye in the thoracic region and the striploin in the lumbar region.
Origin and insertion
Ilium, sacrum, vertebral processes and ribs; each bundle spans one or several segments.
Action
Extend and stabilise the vertebral column. Acting on one side only, they bend it laterally. They also raise the head and neck.
Innervation
Dorsal branches of the spinal nerves.
Clinical relevance
- In paravertebral anaesthesia of the flank, spinal nerves T13, L1 and L2 are blocked next to the lumbar transverse processes; the needle passes through these muscles. The inverted-L block infiltrates along the caudal border of the last rib and ventral to the lumbar transverse processes.
- Rib eye area, measured at the cut between ribs 12 and 13, is used in carcass grading to estimate lean meat yield.
- Blackleg (Clostridium chauvoei) can affect the large muscle masses of the back and loin in young cattle, as well as those of the hindquarter and shoulder.