On the variability of the human flocculus and paraflocculus accessorius

42 human cerebelli were examined macroscopically in order to ascertain the general morphological, conformation of the flocculus and accessory paraflocculus, as well as their variability. The flocculus had a mean number of 14.2 +/- 0.3 (s.e.) folia and 7.0 +/- 0.4 (s.e.) subfolia arranged in a rosette-like cluster of relatively constant shape. The coefficient of variability of the number of folia and subfolia was respectively 22.1% and 47.4%. The accessory paraflocculus had a mean number of 4.2 +/- 0.2 (s.e.) folia and 2.0 +/- 0.2 (s.e.) subfolia, with a variability coefficient of respectively 50.2% and 102.8% which was more than double that of the flocculus. In fact the conformation of the accessory paraflocculus varied from a single small flattened lamella to a rosette-like cluster of folia similar in shape and size to those of the flocculus. There was no correlation between the variability of the flocculus and accessory paraflocculus. The possible reason for this marked variability is discussed in the light of the phylogenetic evolution of the structures examined.