216 ARTICULATIONS. 



considerable. When the fibro-cartilage is perforated, the synovial membrane is 

 continuous with that which lines the wrist. 



Actions, The movement which occurs in the inferior radio-ulnar articulation is 

 just the reverse of that which takes place between the two bones above ; it is 

 limited to rotation of the radius round the head of the ulna ; rotation forwards 

 being termed pronation, rotation backwards supination. In pronation, the sigmoid 

 cavity glides forward on the articular edge of the ulna ; in supination, it rolls in 

 the opposite direction, the extent of these movements being limited by the anterior 

 and posterior ligaments. 



7. WKIST-JOINT. 



The Wrist presents most of the characters of an enarthrodial joint. The parts 

 entering into its formation are, the lower end of the radius, and under surface of 

 the triangular interarticular 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 sub- 

 divided 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 follow- 



ing ligaments. 



External Lateral. Anterior. 



Internal Lateral. Posterior. 



The External Lateral Ligament 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 is a rounded cord, attached, above, to the ex- 

 tremity of the styloid process of the ulna ; below, it divides 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 fasci- 

 culi, 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 digitorum and 

 Flexor longus pollicis ; behind, with the synovial membrane of the wrist-joint. 



The Posterior Ligament, less thick and strong than the anterior, is attached, 

 #bove, to the posterior border of the lower end of the radius ; its fibres descend 

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

 scaphoid, semilunar, and cuneiform bones, its fibres being continuous with those 

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

 extensor tendons of the fingers ; in front, with the synovial membrane of the 

 wrist. 



The Synovial Membrane lines the under surface of the triangular interarticular 

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

 mentioned. 



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 ascend- 

 ing branches from the deep palmar arch. 



The Nerves are derived from the ulnar. 



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



