Thinking backwards about "extends"

Hi, this may sound stupid, but I have a question that I didn’t know that I had…:

A very simple example: a class ChessHorse that extends Sprite, so it inherits its interface. The class constructor creates a Sprite myHorse with a horse picture in it.

If I want the horse sprite to move, I use its Sprite’s properties, like **myHorse.x=250 **.

I can do that because myHorse IS a Sprite, but the instance of the class ChessHorse should inherit the Sprite posibilities, shouldn’t it?

So why I cant just write ChessHorseInstance.x=250?

I am sure that I have skipped something in the understanding of the class concept. Can someone enlighten me, please?

Regards!!