Definition of "brainpan"

Many a time but for a Sallet, my braine-pan had bene cleft with a brown Bill.

1591 (date written), William Shakespeare, “The Second Part of Henry the Sixt, […]”, in Mr. William Shakespeares Comedies, Histories, & Tragedies. […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act IV, scene ix]

Yet, whether thwart or flatly it did lyte, / The tempred steele did not into his braynepan byte.

1596, Edmund Spenser, “Book VI, Canto VI”, in The Faerie Queene. […], London: […] [John Wolfe] for William Ponsonbie

‘And a hard word it is,’ said Richie, ‘as my brainpan kens to this blessed moment.’

1822, Walter Scott, The Fortunes of Nigel