Abstract
1. The relative development of the motor facial nucleus was studied, using brain specimens of 91 species of animals, including 83 mammals, the domestic fowl (cock and hen), 6 reptiles and a frog.
2. The relative development of the nucleus was determined by the ratio of the total number of the cells in the right and the left halves of the nucleus counted on the serial transverse sections of the above specimens to the area of the tegmentum of the brain stem at a certain level.
3. In the non-mammalian animals, the relative number of the cells in the motor facial nucleus is very small.
4. The relative number in the mammals was small in the order of Monotremata, generally large in Marsupialia, Insectivora, Chiroptera and Rodentia and moderately large in Cetacea, Ungulata, Carnivora and Prosimiae. In higher Primates it is small and particularly small in man. In Edentata also it is generally small.
5. A comparative study of the findings has revealed that the development of the motor facial nucleus depends more on the development of the platysma than on that of the face musculature.
