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
Anatomy of the cerebellum posterior inferior portion of the cerebellum, the inferior cerebellar peduncle, the nucleus ambiguus, the vagus motor nucleus, the spinal trigeminal nucleus, the solitary nucleus, and the vestibulocochlear nuclei. There is considerable variation in the size and shape of the cerebellum in different vertebrate species. It is generally largest in cartilaginous and bony fish, birds, and mammals, but somewhat smaller in reptiles. The large paired and convoluted lobes found in humans are typical of mammals, but the cerebellum is generally a single median lobe in other groups, and is either smooth or only slightly grooved. In mammals, the neocerebellum is the