THE EVOLUTION AND ANATOMY OF THE CEREBELLUM

Observing that the ‘hemispheres’ are essentially a mammalian structure, Edinger (1910) applied the term ‘palaeocerebellum’ to the vermis and flocculus and the term ‘neocerebellum’ to the remainder (Fig. 3). Hausman (1929), elaborating on this concept, stated that a neocerebellar equivalent has been provided for each lobule of the vermis except the lingula. Although useful and expressive, the terms neo‐ and palaeocerebellum have been used by many different authors to designate somewhat different cerebellar parts, and unless qualified or limited have at present no certain meaning. Further, as Winkler (1923) and others have emphasized repeatedly, new acquisitions to the cerebellum take the form of growth of preexisting parts rather than altogether new structures superimposed on the old. The identification of the vermis, as defined by Edinger, as a morphological entity is misleading and lacks morphological or functional support. Hausman's identification of all lateral cerebellar parts with the neocerebellum seems hardly justified when we realize that both ontogenetically and phylogenetically the cerebellum had a bilateral origin, and that even in man one of the lateral parts, the flocculus, appears very early in the development of the cerebellum. The term neocerebellum has some meaning if reserved for those parts which in the higher mammals have come to be dominated by cortico‐pontine connexions; but such a definition allows for no hard and fast delimitation by particular fissures. If the rest of the cerebellum is then designated palaeocerebellum, it must be recognized that it contains subdivisions of varying phylogenetic age.