Sesamoiitis is inflammation of the sesamoid bones. In humans it occurs on the bottom of the foot, just behind the large toe. There are normally two sesamoid bones on each foot; sometimes sesamoids can be bipartite, which means they each comprises two separate pieces. The sesamoids are roughly the size of jelly beans. In humans the sesamoid bones act as a fulcrum for the flexor tendons, the tendons which bend the big toe downward.