During the past fifteen years various writers have developed the conception of fiber tracts within peripheral nerves analogous to those in the spinal cord and brain. That is, in a given nerve, the fibers that supply a certain muscle or a certain area of the skin have been thought to be situated constantly within a definite region of the trunk of the nerve at a given level. Thus, the anatomist Bardeen,1 from his observations on the segmental distribution of the peripheral nerves of the lower extremity in the embryo and his dissections of nerve trunks in the adult, comes to the conclusion that, though nerves are made up of anastomosing bundles of fibers, the actual course of the fibers is for the most part a straight one from the plexus to the point where a peripheral branch is given off. Further, he thought that a given segmental level of