Riddle 39

My first was a scholarly Scotchman of note,
Discourses and essays he learnedly wrote,
My second was found in the post, such a scrawl!
That letter never was opened at all.
My third ’s made of flesh and sinew and bone,
My first, I suppose had two of his own;
My whole is a man delightful to folks
Who enjoy reading jocular jingles and jokes.