Division of Grey Matter, the Rearmost Part
Puzzle 7 of Sherlock Holmes Hard Pack
Question is: Division of Grey Matter, the Rearmost Part
and the answer is: HINDBRAIN
Word Meaning:
HINDBRAIN — (neuroanatomy) The posterior part of the brain, comprising the cerebellum, pons and medulla, the rhombencephalon
Definitions from Wiktionary.