The
Weberian apparatus is an anatomical structure that connects the
swim bladder to the
auditory system in
fishes belonging to the Superorder
Ostariophysi. When it is fully developed in adult fish, the elements of the apparatus are sometimes collectively referred to as the
Weberian ossicles. The presence of the structure is one of the most important and phylogenetically significant distinguishing characteristics of the Ostariophysi. The structure itself consists of a set of minute bones that originate from the first few
vertebrae to develop in an embryonic ostariophysan. These bones grow to physically connect the auditory system, specifically the
inner ear, to the swim bladder. The structure acts as an amplifier of sound waves that would otherwise be only slightly perceivable by the inner ear structure alone.