Anatomy of the cerebellum major part of the cerebellum by mass, but in other vertebrates, it is typically the spinocerebellum. In amphibians, lampreys, and hagfish the cerebellum is little developed; in the latter two groups it is barely distinguishable from the brain-stem. Although the spinocerebellum is present in these groups, the primary structures are small paired nuclei corresponding to the vestibulocerebellum. The cerebellum follows the general groups-of-three pattern found in anatomy, with three major input and output cerebellar peduncles (fiber bundles). These are the superior (brachium conjunctivum), middle (brachium pontis), and inferior (restiform and juxtarestiform bodies) cerebellar peduncles. There are three sources of input
Cerebellum transform sensory inputs in some sophisticated way, perhaps to compensate for changes in body posture. In fact, James M. Bower and others have argued, partly on the basis of these structures and partly on the basis of cerebellar studies, that the cerebellum itself is fundamentally a sensory structure, and that it contributes to motor control by moving the body in a way that controls the resulting sensory signals. Despite Bower's viewpoint, there is also strong evidence that the cerebellum directly influences motor output in mammals. Even the earliest anatomists were able to recognize the cerebellum by its distinctive appearance. Aristotle