LUMBO-SACRAL JOINTS. _ 981 
with a definite capsule (Fig. 218), of which the palmar and cord-like lateral portions 
~ are well marked, while on the dorsal aspect the extensor tendons act as the chief 
a BR ee ee ee od | 
} 
| 
support. The palmar ligaments are fibrous plates of considerable thickness, and 
are attached to the two lateral ligaments and to the intervening rough surface on 
the distal phalanges, while their proximal margins are not attached to bone. Each 
ligament has its lateral margins prolonged proximally to the adjacent sharply- 
defined lateral ridges on the phalangeal shafts. 
The lateral ligaments (Fig. 218) are strong, rounded, short bands, continuous with 
the preceding, and attached to adjacent non-articular lateral aspects of the phalanges. 
Each joint possesses a synovial membrane which lines its capsule, but its 
arrangement presents no special peculiarity. 
MOVEMENTS OF THE CARPAL, INTERMETACARPAL, METACARPO-PHALANGEAL 
AND INTERPHALANGEAL JOINTS. 
The amount of movement which is possible at imdividual joints of the intercarpal, inter- 
metacarpal, and carpo-metacarpal series is extremely limited, both on account of the interlocking 
nature of the articular surfaces and the restraining character of the ligamentous bands. Taken 
as a whole, however, the movements of the carpus and metacarpus enable the hand to perform 
many varied and important functions. This is largely due to the greater mobility of those joints 
on the radial and ulnar borders of the hand, as well as to the general elasticity of the arches 
formed by the carpus and metacarpus. These conditions particularly favour the movements of 
opposition and prehension. In the opposite direction, z.e. when pressure is applied from the 
palmar aspect, the metacarpal and carpal arches tend to become flattened, but great elasticity is 
imparted by the tension of the various hgaments. 
The four inner metacarpo-phalangeal joints are ball-and-socket joints, and movements of 
palmar-flexion and extension are freely performed about a transverse axis. In exceptional cases 
a certain amount of dorsi-flexion is possible. About an antero-posterior axis movements occur 
which are usually referred to the middle line of the hand, and hence called abduction and 
adduction. 
The movements of the index finger are less hampered than in the case of the others, but 
each of them can perform a modified kind of circumduction. 
The metacarpo-phalangeal joint of the thumb and all the interphalangeal joints are uniaxial 
or hinge-joints acting about a transverse axis, which permits of palmar-flexion and extension 
being freely performed, but dorsi-flexion is, as a rule, entirely prevented by the palmar and lateral 
ligaments. 
ARTICULATIONS AND LIGAMENTS OF THE PELVIS. 
Although we may consider the pelvis as a separate part of the skeleton, yet it 
is essential to remember that the bones which enter into its composition belong to 
the spinal column (sacrum, coccyx) and the lower limb (innominate bone). Accord- 
ingly, the articulations, with their corresponding ligaments, may be arranged as 
follows :— 
(a) Those by which the segments of the coccyx are joined together (already 
described, v. p. 256); 
(b) That by which the sacrum articulates with the coccyx (already de- 
seribed, v. p. 256); 
(c) Those by which the sacrum articulates with the last lumbar vertebra 
(Lumbo-sacral joints) ; 
(d) Those by which the innominate bones are attached to the spinal 
column (Sacro-iliac joints) ; 
(e) That by which the innominate bones are attached to each other (Sym- 
physis pubis). 
LUMBO-SACRAL JOINTS. 
The articulation of sacrum with the fifth lumbar vertebra is constructed 
precisely on the principle of the articulations between two typical vertebrie, and 
the usual ligaments associated with such joints are repeated. There is, however, an 
additional accessory ligament, termed the lateral lumbo-sacral ligament (Fig. 219). 
This extends from the front of the inferior border of the transverse process of the 
