The distinguishing characters of these bones have already been noticed (p. 105;.
Looked at from behind the phalanges are rounded and cylindrical in appearance, enlarged at their ends, but on their palmar surfaces they are flattened and bounded by sharp margins on each side. The rounded dorsal surfaces are covered by the expansions of the extensor tendons, while the flat, anterior surfaces form the bony bed of the flexor tendons, against which they are held by the fibrous sheath that is fastened to the margins of the bones.
The first phalanx is attached to the metacarpal as already described, and the inter-phalangeal joints are formed on the same plan, save that there is of course no representative of the transverse metacarpal band. Thus we find rounded facets on the sides of the distal extremities for the lateral hgaments and ligamentous markings on the proximal ends for these and for the capsules in front.
The presence of condyles with intervening depressions in the interphalangeal articulations indicates that there can be no lateral movements in these joints, and the lateral ligaments are attached at what is practically the centre of movement in flexion and extension, so that they are constantly tense.
The dorsal expansion covers the articulations behind and is attached to the bases of the last two phalanges, making a well-marked roughness there, which is therefore not ligamentous.
The theca which holds down the flexor tendons, is not a continuous fibrous layer, but is made up of bands (Fig. 94), so that the markings for it on the bones are irregular. On the first phalanx they are on the margins : the fines of attachment then cross the capsule and lateral ligaments to reach the margins of the second phalanx, then pass on to the third where they meet, more or less fused with the rough basal ridge that marks the insertion of the Flexor profundus tendon. The markings for the different bands that compose the sheath cannot be recognised with any certainty on the bone, but it can be noticed that the upper crucial fibres cause a roughness on the first phalanx behind the line of its margin.
Between the margins the bones are covered by the synovial sheath of the tendons, and on the second phalanx the markings of insertion of Flexor sublimis are easily seen, distinct from the marginal sheath marking, opposite the middle and proximal parts of the shaft.
Where the capsules of the interphalangeal joints support the tendons they are thickened into a single sesamoid body which occupies the anterior notch between the condyles of the phalanges : this raises the tendons shghtly from the bones to which they are going, and so far increases their power of action on these bones.
The last phalanges have a distal expansion that lies under the nail, but its greater thickness is on the palmar surface, where it is roughened by the attachment of the fibro-fatty pad that makes the palmar finger-tip.
The strong phalanges of the thumb are in general similar to the first and last phalanges of the other fingers, but it should be noticed that the base of the first phalanx exhibits a shght central prominence in front which resembles the inter-condylar point on the bases of the second phalanges of the other fingers. This is probably associated with the large size of the sesamoids in the joint and the fact that the intercornual notch in the first metacarpal is more horizontally placed than in the other bones, so that the phalanx fits, in its front part, for practical purposes on two badly-formed condyles.
The phalanges of the hand are much stronger than those of the foot, for they are used as opponents in grasping, whereas httle weight is thrown on the foot bones, except in the case of the big toe. So the appearance of the two classes of bones, conforming with this, is enough (Fig. 85) to enable one to distinguish between them at a glance.