Coracoids

Coracoids are elements of the shoulder or pectoral girdle found in many vertebrates. In tetrapods, the coracoid is typically a distinct bone that lies on the ventral side of the shoulder girdle and participates in articulations with the sternum and the scapula, contributing to the stability and mobility of the forelimb. In some lineages, the coracoid forms part of a scapulocoracoid unit and may fuse with neighboring elements during development or evolution.

In birds, the coracoid is a particularly robust bone that serves as a key structural brace for the wing. It usually connects the sternum ventrally to the scapula dorsally and to the humerus, helping transmit wing muscle forces to the trunk during flight. The coracoid, along with the sternum and furcula, is part of the major supportive framework of the avian shoulder.

In mammals, including humans, the term often refers to the coracoid process, a hook-like projection on the scapula rather than a separate bone. The coracoid process provides attachments for several muscles (such as pectoralis minor, coracobrachialis, and the short head of biceps brachii) and ligaments, contributing to shoulder stability and movement. Fractures or displacement of the coracoid process can occur, though they are relatively uncommon.

In paleontology, coracoids are frequently preserved as distinct elements in fossil shoulder girdles and help distinguish taxa. Their presence, size, and articulation patterns illuminate the evolution of forelimb function across extinct groups.

Overall, coracoids describe a key component of the pectoral girdle with significant functional and evolutionary importance across vertebrates.