Shapes and sizes of different mammalian cerebella. A study in quantitative comparative neuroanatomy.

The shape of the cerebellar cortex in fourteen mammalian species and one bird was studied by careful dissection, counts of the numbers of folia, and measurement of their length. All mammalian cerebella conformed to the same general plan, with an anterior region where folia are continuous between right and left, and three separate posterior appendages. There were, however, considerable differences between species, both in the relative length of the posterior appendages and in the relative abundance of folia on the midline compared to the lateral portions. In order to discover general laws referring to the width and length of the cerebellar cortex in their relation to body weight, cerebellar weight, and area of cerebellar cortex, an allometric analysis was performed. By plotting the values for the various species on log-log diagrams, the following statements can be inferred: 1. The weight of the cerebellar cortex is proportionate to the body weight to the power of 0.72, well comparable to the classical proportionality between brain weight and body weight to the power of 2/3 (Jerison 1973). 2. Cerebellar area and cerebellar weight are proportionate in larger animals, but in the smaller species the thickness of the cerebellar cortex varies and therefore a different dependence is valid. 3. The width of the cerebellar cortex increases with body size in the smaller species but tends to remain constant in the larger ones. 4. The longest anterior-posterior extension in our collection was measured in the bovine cerebellum. 5. The position of man in our collection of species is particular in several ways. The width of the human cerebellum is far greater than allometric relations established for the other species would suggest. Also, the vermal length of man falls short of the allometric rule established for the other species.