Spock the centaur is . . . fascinating.
He's half horse and half Vulcan. Specifically, Spock is the front end of a Vulcan and the back end of a horse. If he was the front end of a horse and the back end of a Vulcan, he would also be a centaur.
Of course, Spock is actually half human. So what we're looking at is one quarter human, one quarter Vulcan, and one half horse.
-via Ace of Spades HQ
Random thought: Perhaps I should write some fan fiction inspired by the Star Trek episode "Let That Be Your Last Battlefield" in which the crew of the Enterprise encounters a bitterly-divided race of centaurs with varying top and bottom halves.