Fraid its not its pedipalp. As you rightly say spiders do have two and they are used during mating, they look like tiny boxing gloves and are either side of the spiders head.near the mouth if you look closely at the picture you can see one on the spiders heads left side ,
just blown the pic up it looks like a shadow, not a leg lol, and for info the two small bits at the rear are its spinneretes used to produce and spread its web