You know, the one that was severed by graverobbers trying to associate his cranial topology with intellectual capacity?
The process of stealing the head was, apparently, not pleasant, since decomposition had set in and the smell was strong (Ed. note: @!!?!?!?!) However, Peter and Rosenbaum succeeded in cleaning the skull and duly carried out their phrenological examination. Peter declared that "the bump of music" in Haydn's skull was indeed "fully developed". Afterward, Peter kept it in a handsome custom-made black wooden box, with a symbolic golden lyre at the top, glass windows, and a white cushion.
Quite seriously, Haydn's skull was pilfered, measured, passed around, hidden in a mattress, left behind for musicologists to show off at dinner parties (I am reminded of a certain fellow by the name of Hannibal), and ultimately only found its way back to the decayed corpse of Haydn in 1954. Nineteen Fifty Four. In other words, for well over a century, the disembodied head of the highly esteemed father of the (Big-C) Classical symphony and the string quartet was being paraded around and gawked at by esteemed musicians at the esteemed Gesellschaft der Musikfreunde in Vienna. I am not making this up. It is entirely plausible that Brahms was able to poke his fingers through poor Haydn's eye sockets, and giggle, even if it's more amusing than it is likely. But if he did, he certainly would have done it with esteem.
In penance for posting a purely Wiki account (however awesomely entertaining it might be), I'll provide you with Haydn's Symphony No. 1, composed 1759 or so. The fledging form of the symphony was actually something rather new-fangled; the ripieno concerto is probably the closest thing we had previously. It sounds a tad ricky-ticky by even Mozartian standards, but remember what a revolution even its grand opening Mannheim crescendo represented. Only three movements here (as the form was modeled largely after the three-movement opera sinfonias of the period), but still following a general fast-slow-fast pattern. Notice the melody + harmony textural characteristic -- Haydn was unafraid of punctuating his counterpoint with full-fledged chords, a far cry from the even- but heavy-handed approach of many Baroque composers. Some day, I fully intend to learn to reliably realize figured bass, but that's more a back-burner goal; I think we're all rather pleased to see the continuo vanish.
In 1759, George Washington got married, and in 1954, the Soviets went nuclear. Sidebar: Who uses the term "eye" to refer to the burner on the stove?