Bones that are the vestigial remains of the 2nd and 4th metacarpal/metatarsal bones. Proximaly they are involved in the carpo-metacarpal and tarso-metatarsal joints, distaly they extend approximatly 3/4 of the way down the cannon bone (3rd metacarpal/metatarsal bone). They are connected to the cannon bone by a broad band of fibrous tissue. A proliferation of bone (periostal reaction) in the region of this fibrous band shows up as a solid protuberance known colloquially as a splint.