Serratus posterior inferior muscle
Musculus serratus posterior inferior
Serratus posterior inferior is a thin, four-sided muscle where the thoracic back meets the lumbar back, pulling on the lower ribs.
At a glance
- English
- Serratus posterior inferior muscle
- Latin (TA2)
- Musculus serratus posterior inferior
- System
- Muscle
- Region
- Back
- Side
- Paired, left and right
- Inserts on
- The eleventh rib, tenth rib and twelfth rib
About the serratus posterior inferior muscle
Serratus posterior inferior lies in the lower back where the thoracic region gives way to the lumbar. It is a thin, irregularly quadrilateral sheet, broader than serratus posterior superior, from which it is separated by a wide gap. It lies under latissimus dorsi and over the erector spinae, and is classed with the intermediate layer of back muscles.
Its origin is a thin aponeurosis on the spines of T11 and T12 and L1 to L2 or L3. This tendinous sheet merges with the thoracolumbar fascia and with the aponeurosis of latissimus dorsi. The fibres run upward and outward, turn fleshy and split into four flat slips that attach to the lower borders of the last four ribs, just lateral to their angles.
By pulling the lower ribs down and back, the muscle helps to fix them against the pull of the diaphragm, and it may assist forced breathing out. It is also described as helping to extend and turn the trunk. Its actual contribution is small, and some authors think its main role is to signal rib position rather than to move the ribs.
It is supplied by ventral rami of T9 to T12, through the lower intercostal and subcostal nerves, and its blood comes from the lower posterior intercostal, subcostal and upper lumbar arteries. Strain of the muscle can give pain over the lower ribs at the back.
Attachments, action and supply
- Origin
- Spines of T11 to L2 or L3, through a thin aponeurosis fused with the thoracolumbar fascia.
- Insertion
- Lower borders of ribs 9 to 12, just lateral to their angles.
- Action
- Draws the lower ribs down and back; helps fix them in breathing and may assist trunk extension and rotation.
- Nerve supply
- Ventral rami of T9 to T12 (lower intercostal and subcostal nerves).
- Blood supply
- Lower posterior intercostal, subcostal and upper lumbar arteries.
Anthromica
See the serratus posterior inferior muscle where it really sits, with every layer of the body around it.
- Every layer, one body. Peel from muscle to bone, nerve, vessel and organ, and turn it any way.
- English and Latin. Every structure named the way your exam names it.
- Quiz until it sticks. Short drills on the structures you keep missing.
Free to start. No card.
