1. The cerebellar nuclei of birds comprise the nuclei medialis, interpositus and lateralis which form single masses respectively and never divide into subnuclei.2. These three nuclei show conspicuous mutual confluence.3. A frank confluence is also observed between the cerebellar nuclei and the nucleus vestibularis. In birds, the nucleus lateralis also comes into the confluence, which was not observed in mammals.4. The estimated ratio of the total area of the maximum cross-sections of the cerebellar nuclei to the area of the maximum cross-section of the cerebellar hemisphere is larger than in mammals other than the monotremata, to which they show similarity in this respect.5. In function, the nuclei lateralis, interpositus and medialis in birds seem to play the part of the nuclei interpositus anterior, interpositus posterior and medialis respectively in the main, and to be concerned with the function of keeping equilibrium, all of them.