The vestibular system of vertebrates is a network of fluid-filled chambers and canals within the bone labyrinth of the inner ear that controls balance and spatial direction. It consists of three orthogonal Semicircular canals that sense angular acceleration and otolith organs that detect gravitational and linear acceleration. Endolymph, a fluid with a density similar to water, moves through sensory hair cells in the ampulla, physically deflecting them and causing a nerve impulse to be initiated. This sensory data is sent to the brain, where it is utilised to manage posture and movement by sending motor commands to skeletal muscle.
The size of Semicircular canals in vertebrates is quite limited. Even animals with vastly different body masses have canals of similar size. Baleen whales, for example, have canals that are barely average in size among mammals. Except in the lowest species, where it is restricted by head size, Semicircular canal size is weakly reliant on body mass throughout vertebrates.