Fig. 52.--1, humerus; 2, ulna; 3, radius. _a_ and _b_, the two medial
collateral ligaments.
Fig. 53.--1, humerus; 2, radius; 3, ulna. _a_, dorsal collateral
ligament; _b_, ventral collateral ligament; _c_, annular ligament.]
Closely connected with the capsule of the joint are the =collateral
ligaments=. The two =medial= collateral ligaments (Fig. 52) arise from
the medial epicondyle. One (_b_) passes distad and laterad to the
interval between the radius and ulna; here it divides, one branch going
to the head of the radius, while the other is attached to the lateral
surface of the ulna at the edge of the semilunar notch. The second
medial ligament (_a_) lies dorsad of the first; it passes to the medial
surface of the ulna, at the distal edge of the semilunar notch.
The two collateral ligaments on the =lateral= side (Fig. 53) arise from
the lateral epicondyle. The ventral one (_b_) passes almost directly
distad and is inserted into the lateral surface of the proximal end of
the radius about one centimeter from the articular surface; its inner
surface is partly united to the annular ligament (_c_) of the radius.
The dorsal one (_a_) is attached to the lateral border of the semilunar
notch of the ulna.
=Articulations of Radius and Ulna.=--The proximal =radio-ulnar
articulation= (Fig. 53) is by a pivot-joint or trochoid. The two bones
are held in place by the =annular= ligament (Fig. 53, _c_). This is
attached on the lateral side to the dorsal border of the radial notch of
the ulna, passes around the head of the radius, receiving some
ligamentous fibres which come from the lateral epicondyle, and is
attached to the coronoid process of the ulna. The annular ligament is
closely united with the capsule of the joint.
The radius and ulna are united for about their middle third by the thin
=interosseous membrane=, which fills the interosseous space between
their adjacent edges.
=The Wrist.=--At the wrist or carpus there are in reality three joints,
the first between the radius and ulna proximad and the first row of
carpals distad, the second between the two rows of carpal bones, the
third between the distal row of carpals and the metacarpals. The first
two are movable joints; the third is not. Each of these three joints has
a capsule, and the bones entering into the joints are interconnected by
numerous ligaments. These ligaments are named by combining the names of
the two bones which they interconnect. Ligaments which interconnect
bones of the same row in the carpus are sometimes distinguished as
=interosseous= ligaments, as contrasted with =intercarpal= ligaments,
which connect together bones of different rows. According to their
position the ligaments may also be distinguished as dorsal, ventral, and
lateral. Detailed descriptions and figures of all these ligaments are
given by Strauss-Durckheim.
=Metacarpals.=--The joint between the carpals and metacarpals has been
described. At the distal end of the metacarpals the articulations with
the phalanges have each a capsule. The joint is further strengthened by
a double lateral ligament on each side. The two sesamoid bones at each
joint are interconnected by a strong transverse ligament, and each is
connected with the head of the metacarpal and the base of the first
phalanx by a lateral ligament.
=Phalanges.=--Between the phalanges the joints possess capsules, and
each has a radial and an ulnar lateral ligament.