146 



ARTICULATIONS OF THE UPPER LIMB. 



Fig. 135. 



is a thick and dense fibro-cartilaginous structure, which is firmly united to 

 the first phalangeal bone, and but loosely adherent to the metacarpal. It is 

 continuous at each side with the lateral ligament, so 

 that the three form one undivided structure which 

 covers the joint, except on the dorsal aspect. Its 

 palmar surface is grooved for the flexor tendon, whose 

 sheath is connected to it at each side : the other sur- 

 face, looking to the interior of the joint, is lined by the 

 synovial membrane, and supports the head of the 

 metacarpal bone. In the joint of the thumb there 

 are two sesamoid bones, one situated at each side, which 

 are connected with its ligaments. 



Fig. 135. LONGITUDINAL ANTERO-POSTERIOR SECTION THROUGH 



THE LOWER PART OP THE RADIUS, THE CARPUS, SEMILUNAR 



BONE, Os MAGNUM, METACARPAL BONE, AND PHALANGES OF 

 THE MIDDLE FINGER, TO SHOW THE SHAPE OF THE ARTI- 

 CULAR SURFACES AND SYNOVIAL CAVITIES BETWEEN THESE 

 SEVERAL BONES. ^ 



1, synovial cavity of the wrist-joint ; 2, intercarpal cavity ; 

 3, carpo-metacarpal cavity ; 4, metacarpo-phalangeal cavity ; 

 5 and 6, phalangeal cavities ; 4', 5', and 6', the palmar fibro- 

 cartilaginous plates which are attached to the base of the several 

 phalanges; 7, indicates the place of the tendons of the long 

 flexor muscles ; 8, a transverse section of the anterior annular 

 ligament ; 9 and 10, transverse retinacula or vaginal ligaments 

 of the flexor tendons on the first and second phalanges. 



A synovial membrane is present in each joint, and 

 invests the surface of the ligaments which connect the 

 bones. 



The phalanges are articulated with one another t on 

 the same plan as that which obtains in the articulations 

 between the bases of the proximal phalanges with the 

 metacarpal bones. 



MOVEMENTS OF THE WRIST AND FINGERS. In the radio-carpal and common carpal 

 articulations, there is allowed not only flexion and extension, but a certain amount of 

 lateral bending. The superior articular surfaces of both ranges of carpal bones being 

 prolonged further on the dorsal than on the palmar aspect, over-extension is allowed 

 in both joints to some degree. In over-extension the opposing surfaces are most per- 

 fectly adapted to each other ; in flexion, they are least so. The kind of movement 

 which is allowed between the carpal and metacarpal bones is best illustrated by placing 

 the hand in such a position that the weight of the body is rested upon the open palm. 

 The metacarpal range, which naturally is concave towards the palm, is flattened ; and 

 the metacarpal inter osseous and palmar ligaments are thus tightened, while a slight 

 separation of the opposed surfaces of the bones takes place ; so also the palmar carpo- 

 metacarpal ligaments are tightened, and both palmar and interosseous ligaments of 

 the second range of carpal bones. The convex part of the os magnum and unciform 

 bone, fitted in those circumstances into the concavity of the first range, is a little wider 

 than the part usually in contact with it; and thus, while the bones of the first range 

 are separated from the distal side, those of the second range are pressed still more 

 separate from the palmar aspect. The whole arrangement secures elasticity. The 

 fourth and fifth metacarpal bones, being more moveable at their carpal articulation 

 than the second and third, bend forward very distinctly in shutting the hand, thus 

 rendering the palm more hollow, and bringing the tips of the fingers more closely 

 together : the movement is one of coaptation. At the phalangeal articulations the 

 only movement allowed is that of flexion and extension, and over-extension is pre- 

 vented by the ligamentous structures in front of the joints. At the metacarpo- 



