In the inferior extremities on the contrary, they are numerous and especially much more evident. Two are seen on each condyle of the femur, in the tendons of the biceps, behind the knee; in front is the patella. In the foot, the tendon of the tibialis posticus near its insertion in the tuberosity of the scaphoid bone, that of the peroneus longus in its passage under the cuboid, have also sesamoid bones. We uniformly see two under the metatarso-phalangeal articulations of the great toe; under most of the analogous articulations of the other toes, they are also found, though they are more variable. In the phalangeal articulations I have also seen them many times. In general, the sesamoid bones exist only in the direction of flexion, which is that in which the greatest efforts to support are made. In the direction of extension I know no one but the patella. These little bones have not, like the others, a separate existence; they are developed always in a fibrous organ, either in a tendon, as those of the biceps, the peroneus, the tibialis posticus, as also the patella; or in a ligament, as all those placed before the metacarpo-phalangeal articulations, the metatarso-phalangeal or phalangeal, which have for their basis the great transverse fibrous fascia, which we have called the anterior ligament of these articulations. _Fibro-Cartilaginous State._ The two primitive bases of the sesamoid bones remain for a long time without exhibiting any rudiments of them, and are at the place where these bones are to exist as they are everywhere else. Their organization is generally uniform. Some time after birth, a little more gelatine than would serve for the nutrition of these two fibrous bodies begins to be exhaled at the place where the sesamoid bones will hereafter be found; then arise cartilages, essentially different from the cartilages of ordinary ossification, which are nearly of the same nature as those of the extremities of the long bones of adults, whilst that these belong truly to the class of fibro-cartilaginous substances. They resemble in their nature the inter-articular fibro-cartilages, those of the tendinous grooves, &c. These are not cartilages, but the fibro-cartilages of ossification, of which we distinguish so much better the fibrous base, as it is nearer the period of their development that we examine them. _Osseous State._