I snapped a small dead branch off of a tree in our back yard today and when I looked at the broken end, there was a spider emerging from a cocoon like sac within the branch. The hollow space inside the branch was 5 mm in diameter. Unfortunately, I was not able to get a photo before the spider had completely emerged from his home. I did take several after he began crawling around (and FAST too!) Can anyone help with an ID? I found the spider about 1:30 PM local time (NDT).

Can anyone tell me the proper term for the 'cocoon'? Is this process called "hatching", "emerging" or what?