Steve Martin and Carl Reiner continue their tour of ancient movie genres with "The Man With Two Brains," which does for Mad Scientist movies what "Dead Men Don't Wear Plaid" did for private eye pictures. Some of the gags depend on a familiarity with classics like "Donovan's Brain," "Bride of Frankenstein" and even, in this case, Mel Brooks' "Young Frankenstein." Other gags depend on Steve Martin's comic personality, as a guy who is playing (a) two bricks short of a load, (b) without a full deck, or (c) with an elevator that doesn't go all the way to the top floor.