A possible source for the opening lines of L'Allegro, apparently unnoted hitherto, is to be found in the opening lines of the last satire in John Marston's Scourge of Villanie:

Sleep grim Reproofe, my iocond Muse doth sing
In other keyes, to nimbler fingering.
Dull sprighted Melancholy, leaue my braine
To hell Cimerian night, in liuely vaine
I striue to paint, then hence all darke intent
And sullen frownes, come sporting meriment,
Cheeke dimpling laughter, crowne my very soule
With iouisance, whilst mirthfull iests controule
The goutie humours of these pride-swolne dayes,
Which I doe long vntill my pen displaies.
0 I am great with mirth, some midwifrie,
Or I shall breake my sides at vanitie.
Roome for a capering mouth, whose lips nere stur,
But in discoursing of the gracefull slur:
Who euer heard spruce skipping Curio
Ere prate of ought, but of the whirle on toe