they are known as tubercles.. from all the reading i've done most believe that they are sensory projections for when they are crawling through tight spaces.. Kind of like antennae or hair like projections to be able to feel out their way through surroundings when hunting at night when vision is not at it's best.
cool, i also heard a theory that it could be since they live in really dry places that in the morning dew would set on them and hey could drink? but that was just a theory a friend said it may be