Complex sentence: In the 1850s it was argued by the scientist Richard Owen that Johnson probably used a recently publicised death mask aleged to be of Shakespeare, a position represented by the painter Henry Wallis in his imaginary scene portraying Ben Jonson showing the death mask to the sculptor.
Split into simpler sentences: In the 1850s it was argued by the scientist Richard Owen that Johnson probably used a recently publicised death mask, which had been claimed to be of Shakespeare. This was depicted by the painter Henry Wallis in his imaginary scene portraying Ben Jonson showing the death mask to the sculptor.