296 ARTICULATIONS. 



form and unciform ; they are continuous with the lateral ligaments of the wrist- 

 joint. 



The common Synovial Membrane of the Carpus is very extensive ; it lines the 

 under surface of the scaphoid, semilunar, and cuneiform bones, sending up- 

 wards two prolongations between their contiguous surfaces ; it is then reflected 

 over the bones of the second row, and sends down three prolongations between 

 them, which line their contiguous surfaces, and invest the carpal extremities 

 of the four inner metacarpal bones. There is a separate synovial membrane 

 between the pisiform and cuneiform bones. 



Actions. The partial movement which takes place between the bones of each 

 row is very inconsiderable ; the movement between the two rows is more 

 marked, but limited chiefly to flexion and extension. 



IX. CARPO-MBTACARPAL ARTICULATIONS. 



1. ARTICULATION OF THE METACARPAL BONE OF THE THUMB WITH THE 



TRAPEZIUM. 



This is an arthrodial joint, which enjoys great freedom of movement, on 

 account of the shape of its articular surfaces, which are saddle-shaped, so that, 

 on section, each bone appears to be received into a cavity in the other, accord- 

 ing to the direction in which they are cut. Hence this joint is sometimes 

 described as one " by reciprocal reception." Its ligaments are a capsular and 

 synovial membrane. 



The capsular ligament is a thick but loose capsule, which passes from the 

 circumference of the upper extremity of the metacarpal bone to the rough 

 edge bounding the articular surface of the trapezium ; it is thickest externally 

 and behind, and lined by a separate synovial membrane. 



2. ARTICULATION OF THE METACARPAL BONES OF THE FINGERS WITH THE 



CARPUS. 



The joints formed between the carpus and four inner metacarpal bones are 

 connected together by dorsal, palmar, and interosseous ligaments. 



The Dorsal Ligaments, the strongest and most distinct, connect the carpal and 

 metacarpal bones on their dorsal surface. The second metacarpal bone receives 

 two fasciculi, one from the trapezium, the other from the trapezoid; the third 

 metacarpal receives one from the os magnum ; the fourth two, one from the os 

 magnum, and one from the unciform ; the fifth receives a single fasciculus from 

 the unciform bone. 



The Palmar Ligaments have a somewhat similar arrangement on the palmar 

 surface, with the exception of the third metacarpal, which has three ligaments, 

 an external one from the trapezium, situated above the sheath of the tendon 

 of the Flexor Carpi Radialis ; a middle one, from the os magnum ; and an in- 

 ternal one, from the unciform. 



The Interos*eous Ligaments consist of short thick fibres, which are limited to 

 one part of the carpo-metacarpal articulation ; they connect the contiguous 

 inferior angles of the os magnum and unciform with the adjacent surfaces of 

 the third and fourth metacarpal bones. 



The Synovial Membrane is a continuation of that between the two rows of 

 carpal bones. Occasionally, the articulation of the unciform with the fourth 

 ami fifth metacarpal bones has a separate synovial membrane. 



The Synovial Membranes of the Wrist (Fig. 203) are thus seen to be five in 

 number. Thejirxt, the membrana sacciformis, lines the lower end of the ulna, 

 the sigmoid cavity of the radius, and upper surface of the triangular inter- 

 articular fibre-cartilage. The second lines the lower end of the radius and 

 intt-rartic.ular fibro-cartilage above, and the scaphoid, semilunar, and cuneiform 

 bones below. The third, the most extensive, covers the contiguous surfaces of 

 the two rows of carpal bones, and, passing between the bones of the second 



