Spinalis thoracis muscle

At a glance

English

Spinalis thoracis muscle

Latin (TA2)

Musculus spinalis thoracis

System

Muscle

Region

Back

Side

Paired, left and right

About the spinalis thoracis muscle

Spinalis is the most medial of the three columns of erector spinae, and its thoracic part, spinalis thoracis or spinalis dorsi, is the only part that is regularly well formed. Even so it is small and hard to separate. It lies against the spinous processes, on the medial side of longissimus thoracis, and is closely fused with it and with semispinalis thoracis beneath.

Its origin is a set of three or four tendons on the spines of T11, T12, L1 and L2. These join into a slim belly that runs up beside the spinous processes. It then divides again into tendons that end on the spines of the upper thoracic vertebrae, with the number of insertions varying from four to eight.

Acting on both sides, the muscle extends the thoracic spine and helps to hold the upper back straight. Acting on one side, it may help to bend the spine to that side. Because it links spine to spine over many levels, it mainly controls the curve of the thoracic spine. It works with longissimus and iliocostalis, which are far larger, and its own share of the force is modest.

Spinalis thoracis is supplied by dorsal rami of the thoracic spinal nerves, and blood comes from the dorsal branches of the posterior intercostal arteries. It is often grouped with the rest of the erector spinae in discussions of back strain and postural pain.

Attachments, action and supply

Origin

Spines of T11 to L2, by several tendons.

Insertion

Spines of the upper thoracic vertebrae, from four to eight in number.

Action

Extends the thoracic spine; on one side may help to bend it to that side.

Nerve supply

Dorsal rami of the thoracic spinal nerves.

Blood supply

Dorsal branches of the posterior intercostal arteries.