intercostobrachialis

The intercostobrachialis is a small muscular or fascial structure located in the upper limb, specifically within the region of the axilla (armpit). Its name derives from its anatomical relationships, with "intercostal" indicating proximity to the intercostal spaces of the thoracic wall and "brachialis" referring to its association with the upper arm. Although not universally recognized as a distinct independent muscle, the intercostobrachialis is often considered a fascia or muscle slip that connects the inner surface of the second or third intercostal space to the medial aspect of the upper arm.

Anatomically, the intercostobrachialis typically originates from the second or third intercostal space in the thoracic wall, near the serratus anterior or intercostal muscles. Its fibers extend obliquely upward and medially to insert onto the medial aspect of the upper arm, near the medial intermuscular septum. This structure may act as a minor flexor or stabilizer of the upper limb and may serve as a conduit for neurovascular structures passing through the axilla.

The intercostobrachialis often corresponds to or overlaps with other fasciae or muscles, such as the medial cutaneous nerve of the arm or nerves contributing to the brachial plexus. It is clinically significant primarily because a variant or injury involving this structure can affect the sensation or motor functions of the medial upper arm.

Overall, the intercostobrachialis is a lesser-known component of the thoracic and axillary anatomy, with a potential role in the structural organization of the upper limb and thoracic wall. Its function and variations are of interest mainly in surgical and anatomical studies.