THE CARPAL JOINTS 237 



ligaments prevents any rotation at the radio-carpal joint, while it permits consider- 

 able freedom of abduction and adduction. 



7. THE CARPAL JOINTS 



The joint;? of the carpus may be subdivided into — 



(a) The joints of the first row. 



(6) The joints of the second row. 



(c) The medio-carpal, or junction of the two rows with each other. 



(a) The Union of the First Row of Carpal Bones 



Class. — Diarthrosis. Subdivision. — Arthrodia. 



The bones of the first row, the pisiform excepted, are united by two sets of 

 ligaments and two interosseous fibro-cartilages. 



Dorsal. Palmar. 



Interosseous fibro-cartilages. 



The two dorsal ligaments extend transversely between the bones, and connect 

 the scaphoid with the semilunar, and the semilunar with the cuneiform. Their 

 posterior surfaces are in contact with the posterior ligament of the wrist. 



The two palmar ligaments extend nearly transversely between the bones 

 connecting the scaphoid with the semilunar, and the semilunar with the cuneiform. 

 They are stronger than the dorsal ligaments, and are placed beneath the anterior 

 ligament of the wrist. 



The two interosseous fibro-cartilages (fig. 235) are interposed between the 

 scaphoid and semilunar, and the semilunar and cuneiform bones, reaching from 

 the dorsal to the palmar surfaces, and being connected with the dorsal and palmar 

 ligaments. They are narrow fibro-cartilages which extend between small portions 

 only of the osseous surfaces. They help to form the convex carpal surface of the 

 ••adio-carpal joint, and are somewhat wedge-shaped, their bases being towards the 

 wrist, and their thin edges between the adjacent articular surfaces of the bones. 



The synovial membrane is a prolongation from that of the medio-carpal joint. 



The arterial and nerve-supplies are the same as for the medio-carpal joint. 



The Union of the Pisiform Bone with the Cuneiform 



This is an arthrodial joint which has a loose fibrous capsule attached to both 

 the pisiform and cuneiform bones just beyond the margins of their articular surfaces. 

 It is lined by a separate synovial membrane. Two strong rounded or flattened 

 bands pass downwards from the pisiform, one to the process of the unciform, and 

 the other to the base of the fifth metacarpal bone; these may be regarded as 

 prolongations of the tendon of the flexor carpi rdnaris, and the pisiform bone may 

 be looked upon in the light of a sesamoid bone developed in that tendon. 



(b) The Union of the Second Row of Carpal Bones 

 Class. — Diarthrosis. Subdivision. — Arthrodia. 



The four bones of this row are united by three dorsal, three palmar, and two 

 interosseous ligaments. 



The three dorsal ligaments (fig. 234) extend transversely and connect the 

 trapezium with the trapezoid, the trapezoid with the magnum, and the magnum 

 with the unciform. 



