Proximal phalanges or singular, "proximal phalanx", are bones found in the limbs of most vertebrates. These bones are classified as having a proximal base, a narrowed shaft, and a distal head like the metacarpal bones. The large metacarpal heads fit into a small concave articular facet at the base of the phalanx forming a mobile joint. Their distal articular surfaces form . These spline-like faces limit the medial and lateral movement of these joints. In humans, they are the bones proximal to the base of a toe or finger, the prominent, knobby ends of which, on the hands, are often called the knuckles. In the average human, there are twenty proximal phalanges in all, ten in the hands (five in each hand) and ten in the feet (five in each foot). The bone they articulate with distally depends on which digit of the hand or foot is being addressed - the proximal phalanx of the thumb as well as that of the big toe articulate with the distal phalanx, while in all the other eight fingers and eight toes the proximal phalanx articulates distally with the intermediate phalanx, or middle phalanx. This is because the thumbs and big toes of humans contain only two phalanges each, while the remaining fingers and toes each contain three. They are palmodorsally flattened bones which are typically more than three times longer than their widest point. The palmar surface is slightly concave and the dorsal surface slightly convex. The proximal phalanges are longer and more massive than the more distal phalanges In other vertebrates, proximal phalanges have a similar placement in the corresponding limbs, be they paw, wing or fin. In many species, they are the longest and thickest phalanx ("finger" bone).