On the show M*A*S*H, which episode featured Hawkeye talking about the number of bones in the human hand and a squirrel?

The episode is 'The Most Unforgettable Characters' from season five.

Hawkeye: This happened while I was in my first year of medical school. I was taking an exam in anatomy. It was really tough. They ask questions like "How many bones are there in the hand?" I was stymied. I kept saying to myself, "How many bones are there in the hand?" Then I heard this little voice that said "24." I looked around the room and there sitting on the window sill of the classroom was this little grey squirrel with a very intelligent face. And he pointed at his hand and said "24." So I wrote it down. And then after the exam I rushed over to the library to look it up. And would you believe it? That stupid squirrel was wrong by four bones. I went looking all over the campus for him. I wanted to kill him. I finally found him over on a bench by the pysche department. "You were wrong!" I screamed at him. "There's 28 bones in the human hand!" "Oh," he said pointing at his hand, "I thought you meant a squirell's hand."
Radar: I don't think I can use that story.
Hawkeye: Want me to make one up?

http://mash.wikia.com/wiki/The_Most_Unforgettable_Characters_(TV_series_episode)

The reference above was from a community forum (now defunct, satguru), but I concur that it is the episode where Radar enrolls in the "Famous Las Vegas Writers School" and is trying to find something to write about.

http://mash.wikia.com/wiki/The_Most_Unforgettable_Characters_(TV_series_episode)