4o8 A MANUAL OF ANATOMY 



though a few pass from the other bones of the second row. The 

 external lateral ligament connects the scaphoid with the trapezium, 

 and the internal lateral connects the cuneiform with the unciform. 



Carpal Synovial Membrane. — This membrane lines the transverse 

 carpal joint, and gives off vertically- disposed processes. Two of 

 these pass upwards, one on either side of the semilunar as far as its 

 interosseous ligaments. Three pass downwards — one between the 

 trapezium and trapezoid, another between the trapezoid and os 

 magnum, and a third between the os. magnum and unciform. There- 

 after the synovial membrane is continued into the inner four carpo- 

 metacarpal joints, and this latter portion of it sends processes into 

 the joints between the bases of the inner four metacarpal bones. 



Arterial Supply.— The anterior and posterior carpal retia. 



Nerve-supply. — The median, ulnar, and posterior interosseous 

 nerves. 



Movements. — The movements between the bones of each row are extremely 

 limited, and are of a gliding nature. The movements at the transverse 

 carpal joint are more free, and take the form of flexion and extension in associa- 

 tion with the corresponding movements at the radio-carpal joint. The 

 number of the carpal articulations imparts to this part of the hand consider- 

 able strength and elasticity, and so enables it to disperse shock. 



Carpo-metacarpal Joints. — Inner Four Joints. — These belong to 

 class diarthrosis, and to the subdivision arthrodia. The bones con- 

 cerned are the trapezium, trapezoid, os magnum, and unciform 

 above, and the bases of the inner four metacarpal bones below. 

 The ligaments are dorsal, palmar, and interosseous. The second, 

 third, and fourth metacarpal bones receive each two dorsal liga- 

 ments as a rule, and the fifth receives one, namely, from the unci- 

 form. The palmar ligaments are usually one to each bone. There 

 is only one interosseous ligament, which connects the adjacent 

 parts of the os magnum and unciform with the inner aspect of the 

 base of the third metacarpal bone towards its palmar aspect. 



The synovial membrane is a continuation of that of the carpus. 



These joints derive their arterial supply from the radial and ulnar 

 arteries, and their nerve-supply from the deep division of the ulnar, 

 and posterior interosseous, nerves. 



Movements. — The movements are those of flexion and extension, the former 

 being most free in the case of the fifth metacarpal, as in the formation of the 

 ' palmar cup.' 



Carpo-metacarpal Joint of the Thumb. — This belongs to the 

 class diarthrosis, and to that variety of the subdivision arthrodia 

 which is called the reciprocal or saddle-joint. The bones which 

 enter into this important joint are the trapezium and the base of^ 

 the first metacarpal. The articular surfaces are saddle-shaped, j 

 and are connected by a capsular ligament, which is attached round! 

 the margin of each articular surface, being strongest on the dorsal 

 and outer aspects. This ligament is sufficiently loose to allow of 

 considerable movement. 



