The splint bones lie adjacent to either the metacarpal or the metatarsal bones (both are the cannon bone depending on whether you are on the pelvic or thoracic limb). There are two for each cannon bone, so as in this picture where they are labeled only one is visible (but another is present opposite it).

In this picture the two splint bones are labeled the second and fourth metacarpals and lie caudal to the third metacarpal (the cannon bone)