JOINTS OF TILE RAND.
Joints of the carpus.—The bones consti tuting each row of the carpus are firmly con nected by strong ligaments, so that their com bined surfaces form one extended surface adapted to the radius, or to the metacarpus, or to each other. Thus the union of the superior articular surfaces of the upper carpal row con stitutes the convex surface that contributes to the formation of the wrist-joint, whilst the united inferior articular surfaces of the same row are adapted to the united superior surfaces of the inferior carpal row. Again, the inferior articular surfaces of this last row enter into the formation of the carpo-metacarpal joints.
The several articulations of each row are strengthened by two sets of ligaments, one on the palmar, the other on the dorsal surface of the joints, palmar and dorsal ligaments; they extend transversely from one bone to the other. The palmar ligaments are considerably stronger than the dorsal. The synovial membranes which exist in these small articulations are merely offsets from the large synovial mem brane which is interposed between the two rows of the carpus.
In the articulation between the scaphoid and lunar bones, as well as in that between the lunar and cuneiform, we observe a remarkable fibro-cartilaginous lamina interposed in the whole extent of each articulation from before backwards, although not extending over the entire articular surfaces. These laminae are readily seen on opening the radio-carpal joint in the interval between the bones above men tioned ; they are attached to the palmar and dorsal ligaments by their anterior and posterior extremities. When dissected out they will be found to he wedge-shaped, the thick edge being directed towards the wrist joint, and adherent to the synovial membrane of that joint. These laminae are described by most anatomists as ligaments, under the name of interosseous liga ments. Of their fibro-cartilaginous nature, however, I have no doubt from repeated and careful examinations; they may therefore be more correctly denominated interosscous fibro cartilages. Feeble interosseous ligaments exist on either side of the os magnum between it and the unciform on one side, and the trapezoid on the other ; they are best seen when these bones are torn from each other.
Articulation of the two rows of carpal bones to each other.—The superior articular surfaces of the four bones composing the inferior carpal row are adapted to the inferior articular surfaces of the scaphoid, lunar, and cuneiform bones. The head of the os magnum and the superior articular surface of the unciform bone form a prominent convexity, which is received into a deep concavity formed on the ulnar side by the cuneiform bone, on the radial side by the scaphoid, and in the centre by the lunar bone; whilst external to the projection of the os mag num, a superficial oblong concavity receives the convexity on the inferior and outer surface of the scaphoid. Thus the line of this articulation has somewhat of the course of the roman S placed horizontally, r4. That part of the arti culation which is to the ulnar side, then, par takes more of the nature of enarthrodia or hall and socket joint, while that to the radial side is arthrodia with almost plane surfaces.
This articulation is strengthened in front by an anterior or palmar ligament which is of considerable strength and thickness. Most of the fibres of this ligament are attached inferiorly to the palmar surface of the os magnum, whence they diverge to he inserted into the scaphoid, lunar, and cuneiform bones; some few fibres extend from the trapezoid and trape zium to the scaphoid, and from the unciform to the cuneiform. Behind we find a dorsal ligament, also strong, although much less so than the palmar. This ligament extends obliquely from the bones of the first row to those of the second, but is stronger on the ulnar than on the radial side. The extent and con nexions of both these ligaments are best seen when the joint is opened, by cutting through the dorsal ligament to view the palmar, and vice versa. The ligaments called lateral by some anatomists are merely the continuation of the lateral ligaments of the wrist-joint; nor do those described by Cruveilhier under the name of glenoid ligaments deserve to be separated from the anterior and posterior, of which they constitute that portion most intimately connected with the anterior and posterior notches of the hollow cavity in which the head of the os mag num is lodged.