four legs good, two legs bad

This image just cracked me up during the lecture. The title, a quote from Animal Farm can help to enlighten it's purpose. But there's quite a salient point to it. On the left is a map of the skin reflecting which nerve is responsible for sensations from that portion of the skin. For example, the thigh is L2 which means the nerve enters the spinal column at the second lumbar vertebra. If you stop and think about it, it becomes a bit puzzling as to why the arms and legs are mixed with different nerves. Why? That's where the goofy picture on the right comes in. When viewed through the lens of a quadraped, the nerves entering the spine in order make perfect sense. It's only odd if viewed through a strictly bipedal fashion. One of the many ways in which the theory of evolution helps to explain biology.