Looks like you were fucking with it or it split from bending your elbows. I would honestly think the damage is done though.
That looks pretty nasty, good call on going to the doctor. When my dad was doing a training exercise for the Army, he was out in the woods for a few days. He got bitten by a brown recluse one night and in the morning felt pretty sick. So he told the rest of his group or whatever to go on and he'd catch up. He ended up becoming confused and disoriented from the fever and got lost. Luckily he happened to run into another group and they got him medical attention. He would have died if he hadn't found them I bet. Haha (This was like 20-30 years ago.)
FUCK BROWN RECLUSES! I had a big problem with them, thankfully I got rid of them. http://forum.grasscity.com/real-life-stories/874295-brown-recluses.html