Birds have a variety of long known anatomical specializations both in the vertebrae and in the spinal cord of lumbosacral segments. In the present investigation additional morphological specializations are described for the pigeon. These consist of segmentally organized semicircular canal-like structures (lumbosacral canals) which together with specializations in the meninges of the spinal cord form a large liquor space above accessory lobes attached to the spinal cord. The whole system is thought to function as a sense of equilibrium. The neurons in the lobes are assumed to be sensory neurons which are stimulated by the inertia of the fluid during movements of the body. Such a function is supported by lesion experiments: opening of the fluid space was followed by severe disturbances of landing and walking behavior.