interclavicles

The interclavicle is a bone found in the pectoral girdle of many tetrapods, particularly in reptiles and amphibians. It is a median bone that lies in the midline of the chest, articulating with the clavicles and sometimes the sternum. Its primary function is to brace the pectoral girdle, providing structural support for the forelimbs.

The presence and form of the interclavicle vary significantly across different groups. In amphibians, it is often cartilaginous or absent. In reptiles, it is typically ossified and well-developed, playing a crucial role in locomotion and defense. For instance, in some lizards, the interclavicle is robust and helps to anchor the shoulder girdle against the body, aiding in quick movements. In turtles, the interclavicle is fused with other elements to form part of the plastron, the ventral shell.

Birds have a highly modified interclavicle, which fuses with the clavicles to form a fused structure known as the furcula or wishbone. This fusion is an adaptation for flight, providing a strong anchor point for the powerful flight muscles of the chest.

In mammals, the interclavicle is generally absent, with the clavicle (collarbone) being the primary bone of the pectoral girdle. However, a small, vestigial interclavicle can be found in some marsupials and monotremes, suggesting its evolutionary history. The interclavicle's presence or absence and its morphological variations are important characteristics used in the phylogenetic classification of vertebrates.