Final answer:
Most medulloblastomas develop in the cerebellum, a part of the rhombencephalon which includes pons and myelencephalon, and is responsible for essential motor controls and balance.
Step-by-step explanation:
Most medulloblastomas, which are cancerous tumors, develop in the cerebellum. The cerebellum is part of the rhombencephalon, which in the developing embryonic brain, gives rise to the metencephalon and myelencephalon. The metencephalon then develops further into the pons and the cerebellum. As such, approximately 90% of medulloblastomas are found in the cerebellum region of the brain, influencing balance, motor control, and other vital functions.