Normal Sagittal MRI Brain Cerebellum Vermis

A 58-year-old male with a 20-year history of alcohol use disorder presents with progressive gait instability and difficulty walking in a straight line. MRI brain shows selective atrophy of the structure marked **B** in the sagittal view. On examination, he has a wide-based gait and incoordination of the legs, but his upper limb coordination and speech are relatively preserved. Which of the following best describes the functional zone affected in this patient?