The bone below the base of the thumb in the foot is called the first metatarsal. Each foot has five metatarsals, the first metatarsal is the longest one, the distal end is the first metatarsophalangeal joint, and the proximal end is the ankle joint formed by the first metatarsal and the medial cuneiform of the foot called the metatarsal joint. The metatarsophalangeal joint is basically at the highest part of the foot arch. You can find the root of the first toe by hooking up the toe and then locating the root of the first toe, which is the location of the first talonavicular joint, where you can see a very obvious protrusion, which is the metatarsal head of the first metatarsal. The area where the first and second metatarsal bones meet is the area where the first metatarsal bone forms a joint with the medial cuneiform bone of the foot, the proximal end of the first metatarsal bone.