Subcostalis Muscles

What Are the Subcostalis Muscles

The subcostalis muscles, also called the subcostales (plural) or subcostals, are thin, short, strap-like skeletal muscles deep in the posterior thoracic wall. They are among the intrinsic muscles of the chest wall, along with the intercostal, transversus thoracis, levatores costarum, and serratus posterior muscles. Together, these muscles help maintain the stability of the thoracic wall and its movements during breathing.

Anatomy

Location and Attachments

Origin	The angle of the ribs, especially on the lower part of the thorax
Insertion	Interior surface and superior border of 1-2 ribs below

Origin

Each subcostal muscle originates from the inner surface of a single rib near its angle. The point of origin often extends to the areas adjacent to the ribs.

These muscles are usually most defined in the lower part of the ribcage, especially from the 7th rib. However, they may display variable anatomy as their total number and attachments can vary from person to person.

Insertion

The fibers of the subcostals run inferomedially, parallel to the fibers of the internal and innermost intercostals. Each muscle inserts into the upper border and inner surface of one or two ribs located immediately below the rib from which it originates. So, they can span over 2 or even 3 intercostal spaces from where they start to where they end. It makes them different from the intercostal muscles that only span a single intercostal space.

Relations With Surrounding Muscles and Structures

The subcostal muscles are located on both sides of the thoracic vertebrae. They have the innermost intercostals on their lateral side, where the two muscles sometimes fuse or blend together. 

The subcostals lie deep to the internal intercostals (both muscles and membranes) and superficial to the parietal pleura and endothoracic fascia. The intercostal nerves and the lower back part of the intercostal arteries and veins lie superiorly.

Function

Action

Depressing the rib cage during forced exhalation

The subcostal muscles work similarly to the internal intercostal muscles. They help lower the ribs at the joints, connecting them to the spine (the costovertebral joints), effectively pulling the ribcage down. This action compresses the lungs, expelling the air during forceful exhalation.

These muscles also support the thoracic wall, rib cage, and intercostal spaces.

Innervation

Nerve

Intercostal nerves

Like most other thoracic wall muscles, subcostals are also innervated by the intercostal nerves. They arise from the T1 to T11 thoracic spinal nerve’s anterior rami, with each nerve supplying the corresponding subcostalis.

Blood Supply

Artery

Posterior intercostal arteries

The primary blood supply of these muscles comes from the posterior intercostal arteries, which run along the upper border of each rib. The intercostal veins take care of their drainage into the superior vena cava.