How do reflector telescopes work?

After watching an episode of nova, I was reminded of a question that has gone unanswered throughout my entire education. A reflector telescope takes in light that filters to a mirror at the base of the telescope. That mirror reflects the light to a mirror just above the main one so that the image may be projected to the eyepiece. So, my question to you is:"Why is there not a shadow cast by the small mirror, which would result in an incomplete image?