Akkadian

muḫḫu - top of the head; brain, marrow (CAD M₂ 172, AHw. 667)

PS
*muḫḫ- - brain, marrow (SED I No. 187; Kogan 2011: 220)

‘Brain’ is the only meaning to develop into ‘top of the head’, ‘head, skulľ, on the one hand, and ‘marrow’, on the other.