For the purpose of these studies 111 cases of the fetus skulls, 25 cases of the juvenile skulls and 220 cases of the adult skulls were used and the following results were obtained; 1. The perfect ring-shaped formation of the foramen rotundum is observed in all cases of the fetuses after the 4th fetal month. The earliest perfect ring-shaped formation of the foramen ovale is observed in the 7th fetal month and the latest in 3 years after birth. The earliest perfect ring-shaped formation of the foramen spinosum is observed in the 8th month after birth and the latest in 7 years after birth. 2. The foramen rotundum is mostly oval-shaped in the fetal period and it is round-shaped in general after birth. The majority of the foramen ovale is oval-shaped and it is irregular in shape compared with the rest of two types of foramina. The majority of the foramen spinosum is round in shape. 3. The average diameter of the foramen rotundum is 3.55 mm in the adult. The average maximal length of the foramen ovale is 7.48 mm and its average minimal length is 4.17 mm in the adult. The average diameter of the foramen spinosum is 2.63 mm in the adult. The differences between the right and left and the sexual differences fail to be observed in all types of foramina.