Distal

The distal or terminal phalanges (singular phalanx) are the terminal limb bones located at the tip of the digits (i.e. fingers and toes). These bones are classified as having a proximal base, a narrowed shaft, and a distal head like the metacarpal bones . Their reduced, flattened heads do not form articular facets. The heads form a rough tuberosity on the palmar surface for attachment of the soft mass of the finger tips. The distal phalanges articulate with the middle phalanges. Each phalangeal base forms a double concave facet with a weak central spline which limits the joint movement to the dorsopalmar plane. In Human Anatomy In human anatomy, the distal phalanges of the four fingers and toes articulate proximally with the intermediate phalanges at the distal interphalangeal joints (DIP); in the thumb and big toe, with only two phalanges, the distal phalanges articulate proximally with the proximal phalanges. The distal phalanges carry and shape nails and claws and are therefore occasionally referred to as the ungual phalanges. The distal phalanges are cone-shaped in most mammals, including most primates, but relatively wide and flat in humans. Fingers The distal phalanges of the fingers are convex on their dorsal and flat on their volar surfaces; they are recognized by their small size, and by a roughened, elevated surface of a horseshoe form on the volar surface of the distal extremity of each which serves to support the sensitive pulp of the finger. In the distal phalanges of the hand the centres for the bodies appear at the distal extremities of the phalanges, instead of at the middle of the bodies, as in the other phalanges. Moreover, of all the bones of the hand, the distal phalanges are the first to ossify. In the hand, the distal ends of the distal phalanges possess flat and wide expansions called apical tufts. They serve to support the fleshy pad or pulp on the volar side of the fingertips and the nails on the dorsal side. The shaft of the distal phalanx is expanded proximally at the base and "waisted" distally. It ends in a crescent-shaped rough cap of bone epiphysis — the apical tuft (or ungual tuberosity/process) which covers a larger portion of the phalanx on the volar side than on the dorsal side. Two lateral ungual spines project proximally from the apical tuft. Near the base of the shaft are two lateral tubercles. Between these a V-shaped ridge extending proximally serves for the insertion of the flexor pollicis longus. Another ridge at the base serves for the insertion of the extensor aponeurosis. The flexor insertion is sided by two fossae — the ungual fossa distally and the proximopalmar fossa proximally. Thumb The human pollical distal phalanx (PDP) has a pronounced insertion for the flexor pollicis longus (asymmetric towards the radial side), an ungual fossa, and a pair of dissymmetric ungual spines (the ulnar being more prominent). This asymmetry is necessary to ensure that the thumb pulp is always facing the pulps of the other digits, an osteological configuration which provides the maximum contact surface with held objects.

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