What is this fitting?

I bought on '05 LJ Rubicon last week. While looking it over closely once I got it home I discovered a rectangular machined steel brake line junction block fastened to the drivers side of the rear axle. It also has a steel tube extending vertically from it with a barb as if to accept a hose. I used a fine wire to extend down into it and it goes down farther than the axle housing wall - as if to serve as an axle housing vent also. Is this a vent and should there be a hose on the barb going somewhere?

Sorry no photo, the light in my garage just wasn't good enough to get a good pic this morning.



Thanks, Don