Coracoid

A coracoid is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (therians = marsupials and placentals). In therian mammals (including humans) it is non-existent or fused with the scapula as the coracoid process.

In other tetrapods it has a notch on the dorsal surface which, along with a similar notch on the ventral surface of the scapula, forms the socket in which the proximal end of the humerus (upper arm bone) is located. The acrocoracoid process is an expansion adjacent to this contact surface, to which the shoulderward end of the biceps brachii muscle attaches in these animals. In birds (and generally theropods and related animals), the entire unit is rigid and called scapulacoracoid. This plays a major role in bird flight.

In fish it provides the base for the pectoral fin (FishBase 2006).