Subcostales

Subcostales, or subcostal muscles, are a small group of thin muscles on the inner surface of the thoracic wall. They form part of the deepest layer of the intercostal muscles and are variably present, typically numbering about five to seven on each side. Located on the posterior and internal aspect of the thoracic cage, they run roughly from the inner surface of one rib to the rib two or more levels below.

Anatomy: Each subcostal muscle originates from the inner surface of the lower border of a rib near its angle and inserts on the inner surface of the rib two or three levels below. They generally extend obliquely downward and medially, crossing two or more intercostal spaces. They are not always complete across all intercostal spaces and may be interrupted by tendinous fibers.

Neurovascular supply: The subcostal muscles are supplied by the corresponding intercostal nerves (ventral rami of thoracic spinal nerves) and receive blood from the posterior intercostal arteries.

Function and clinical notes: They assist in depressing the ribs during forced expiration and help stabilize the thoracic wall; their small size and variability mean they are usually of minor functional significance and may be absent or small in some individuals. They are encountered in anatomical dissections and thoracic surgical procedures, and injuries to the subcostal region can affect nearby structures.