294 ARTICULATIONS. 



VII. WRIST-JOINT. 



The Wrist presents some of the characters of an enarthrodial joint, but is 

 more correctly regarded as an arthrodia. The parts entering into its formation 

 are, the lower end of the radius, and under surface of the triangular interar- 

 ticular fibro-cartilage above ; and the scaphoid, semilunar, and cuneiform bones 

 below. The articular surfaces of the radius and interarticular fibro-cartilage 

 form a transversely elliptical concave surface. The radius is subdivided into 

 two parts by a line extending from before backwards ; and these, together with 

 the interarticular cartilage, form three facets, one for each carpal bone. The 

 three carpal bones are connected together, and form a convex surface, which is 

 received into the concavity above mentioned. All the bony surfaces of the 

 articulation are covered with cartilage, and connected together by the following 

 ligaments : 



External Lateral. Anterior. 



Internal .Lateral. Posterior. 



The External Lateral Ligament (radio-carpal) (Fig. 201) extends from the 

 summit of the styloid process of the radius to the outer side of the scaphoid, 

 some of its fibres being prolonged to the trapezium and annular ligament. 



The Internal Lateral Ligament (ulno-carpal) is a rounded cord, attached, above, 

 to the extremity of the styloid process of the ulna; and dividing below into two 

 fasciculi, which are attached, one to the inner side of the cuneiform bone, the 

 other to the pisiform bone and annular ligament. 



The Anterior Ligament is a broad membranous band, consisting of three fas- 

 ciculi, attached, above, to the anterior margin of the lower end of the radius, its 

 styloid process, and the ulna; its fibres pass downwards and inwards, to be 

 inserted into the palmar surface of the scaphoid, semilunar and cuneiform bones. 

 This ligament is perforated by numerous apertures for the passage of vessels, 

 and is in relation, in front, with the tendons of the Flexor Profundus Digito- 

 rum and Flexor Longus Pollicis ; behind, with the synovial membrane of the 

 wrist-joint. 



The Posterior Ligament (Fig. 202), less thick and strong than the anterior, is 

 attached, above, to the posterior border of the lower end of the radius; its fibres 

 pass obliquely downwards and inwards to be attached to the dorsal surface of 

 the scaphoid, semilunar, and cuneiform bones, being continuous with those of 

 the dorsal carpal ligaments. This ligament is in relation, behind, with the ex- 

 tensor tendons of the fingers; in front, with the synovial membrane of the wrist. 



The Synovial Membrane (Fig. 203) lines the under surface of the triangular 

 interarticular fibro-cartilage above ; and is reflected on the inner surface of the 

 ligaments just described. 



Relations. The wrist-joint is covered in front by the flexor, and behind by 

 the extensor tendons ; it is also in relation with the radial and ulnar arteries. 



The arteries supplying the joint are the anterior and posterior carpal 

 branches of the radial and ulnar, the anterior and posterior interosseous, and 

 some ascending branches from the deep palmar arch. 



The nerves are derived from the ulnar. 



Actions. The movements permitted in this joint are flexion, extension, ab- 

 duction, adduction, and circumduction. It is totally incapable of rotation, one 

 of the characteristic movements in true enarthrodial joints. 



VIII. ARTICULATIONS OF THE CARPAL BONES. 



These articulations may be subdivided into three sets : 



1. The Articulations of the First Row of Carpal Bones. 



2. The Articulations of the Second Row of Carpal Bones. 



3. The Articulations of the Two Rows with each other. 



