It looks like that could be the old-school roller-cam brake? I could be wrong and it might just be canti's mounted upside down. But now I am getting nostalgic...

This type of brake was popular in the early 90's on mtb bikes. I think it fell out of favor because, obviously, that location is subject to receiving a tremendous amount of mud. Also, the brake was hard to adjust.

The cam was actually a plate with a special curve on the edges and the brake levers had rollers that followed the profile of the cam. When you applied your brake, the cam would pull out, and the rollers followed the profile to actuate the brakes. The nice thing about it is that the profile allowed for drastic increase of mechanical advantage as a function of cam position (ie mechanical advantage increases as you squeeze the brake harder).

It was cool for a while, then canti's got more popular, followed by v-brakes and disks.