The Intermediate Back Muscles

Original Author: Oliver Jones
Last Updated: March 23, 2017
Revisions: 20

The muscles of the back can be divided into three groups – superficial, intermediate and intrinsic:

  • Superficial – associated with movements of the shoulder.
  • Intermediate – associated with movements of the thoracic cage.
  • Deep – associated with movements of the vertebral column.

The deep muscles develop embryologically in the back, and are thus described as intrinsic muscles. The superficial and intermediate muscles do not develop in the back, and are classified as extrinsic muscles.

This article is about the anatomy of the intermediate back muscles – their attachments, innervations and functions.


The intermediate group contains two muscles – the serratus posterior superior and serratus posterior inferior. These muscles run from the vertebral column to the ribcage, and assist with elevating and depressing the ribs. They are thought to have a slight respiratory function.

Fig 1.0 - The serratus posterior inferior.

Fig 1.0 – The serratus posterior inferior.

Serratus Posterior Superior

The serratus posterior superior is a thin, rectangular shaped muscle. It lies deep to the rhomboid muscles on the upper back.

  • Attachments: Originates from the lower part of the ligamentum nuchae, and the cervical and thoracic spines (usually C7 – T3). The fibres pass in an inferolateral direction, attaching to ribs 2-5.
  • Innervation: Intercostal nerves.
  • Actions: Elevates ribs 2-5.

Serratus Posterior Inferior

The serratus posterior inferior is broad and strong. It lies underneath the latissimus dorsi.

  • Attachments: Originates from the thoracic and lumbar spines (usually T11 – L3). The fibres pass in a superolateral direction, attaching to ribs 9-12.
  • Innervation: Intercostal nerves.
  • Actions: Depresses ribs 9-12.

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Question 1 / 5
Which group of muscles in the back arise from within the back embryologically?

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Question 2 / 5
Which muscle of the back elevates ribs 2-5?

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Question 3 / 5
What is the innervation of the intermediate muscles of the back?

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Question 4 / 5
Serratus posterior inferior depresses which ribs?

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Question 5 / 5
What is the relationship of serratus posterior superior to the rhomboids?

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