_l.u._, External, _l.r._, internal, lateral ligament; _Cr_, radial
carpal; _Ci_, intermediate carpal; _Cu_, ulnar carpal; _C2_, second
carpal; _C3_, third carpal; _C4_, fourth carpal; _Mc2_, second
(internal) metacarpal; _Mc3_, third (large) metacarpal; _Mc4_,
fourth (external) metacarpal.
]
The =synovial membrane= forms three sacs corresponding to the three
joints. The =radio-carpal sac= is the most voluminous; it includes the
joints formed by the accessory carpal bone, and also those between the
proximal carpal bones as far as the interosseous ligaments. The
=intercarpal sac= sends extensions upward and downward between the bones
of the two rows as far as the interosseous ligaments; it communicates
between the third and fourth carpal bones with the =carpo-metacarpal
sac=. The latter is very limited in extent, and is closely applied to
the bones; it incloses the carpo-metacarpal joint, and lubricates also
the lower parts of the joints between the distal carpal bones and the
intermetacarpal joints.
The =external lateral ligament= (Ligamentum carpi collaterale ulnare) is
attached above to the external tuberosity of the distal end of the
radius. Its long superficial part is attached below to the proximal end
of the external small metacarpal chiefly, but some fibers end on the
large metacarpal bone. A canal for the lateral extensor tendon separates
a short deep band which ends on the ulnar carpal bone. Other deep fibers
connect the latter with the fourth carpal bone, and the fourth carpal
with the metacarpus.
The =internal lateral ligament= (Ligamentum carpi collaterale radiale)
resembles the preceding in general, but is stronger and wider distally.
It is attached above to the internal tuberosity of the distal end of the
radius and ends below on the proximal ends of the large and inner small
metacarpal bones. Deep fasciculi are detached to the radial and second
carpal bones. The first carpal bone, when present, is usually embedded
in the posterior part of the distal end of the ligament. The posterior
part of the ligament is fused with the posterior annular ligament
(Ligamentum carpi transversum), and concurs in the formation of a canal
for the tendon of the flexor carpi internus.
A number of special short ligaments connect two or more adjacent
bones; only the most distinct of these will be described here.
The accessory carpal bone is connected with adjacent bones by three
ligaments (Fig. 444). The proximal one is a short band which extends
from the accessory carpal in front of the groove on its outer face and
is inserted into the distal end of the radius behind the groove for
the lateral extensor tendon. A middle band connects the accessory with
the ulnar carpal. The distal ligament consists of two strong bands
which pass from the lower margin of the accessory to the fourth carpal
and the proximal end of the outer metacarpal bone; these bands
transmit the action of the muscles, which are inserted into the
accessory carpal bone. The other bones of the proximal row are
connected by two anterior or dorsal ligaments, which are transverse in
direction, and two interosseous ligaments. An oblique ligament passes
from an eminence on the posterior surface of the radial carpal bone to
a small depression on the radius internal to the facet for the
accessory carpal bone.
Two ligaments connect the proximal and distal rows posteriorly. The
inner one joins the radial to the second and third carpal, and the
outer one attaches the ulnar to the third and fourth carpals.
The bones of the distal row are connected by two strong transverse
anterior or dorsal ligaments and two interosseous ligaments.
There are four carpo-metacarpal ligaments. Two oblique anterior bands
connect the third carpal with the large metacarpal. Two interosseous
ligaments pass downward from the interosseous ligaments of the distal
row to end in depressions in the interstices between the proximal ends
of the metacarpal bones.
[Illustration: