WRIST JOINT. 141 



border of the interosseous ligament. This ligament affords an exten- 

 sive surface for the attachment of muscles. 



The interosseous ligament is in relation, in front, with the flexor 

 profundus digitorum, the flexor longus pollicis, and pronator quadratus 

 muscle, and with the anterior interosseous artery and nerve ; and be- 

 hind with the supinator brevis, extensor ossis metacarpi pollicis, ex- 

 tensor primi internodii pollicis, extensor secundi internodii pollicis, and 

 extensor indicis muscle, and near the wrist with the anterior inter- 

 osseous artery and posterior interosseous nerve. 



The anterior inferior ligament is a thin fasciculus of fibres, passing 

 transversely between the radius and ulna. 



The posterior inferior ligament is also thin and loose, and has the 

 same disposition on the posterior surface of the articulation. 



The inter articular, or triangular fibro-cartilage, acts the part of a 

 ligament between the lower extremities of the radius and ulna. It is 

 attached by its apex to a depression on the inner surface of the styloid 

 process of the ulna, and by its base to the edge of the radius. This 

 fibro-cartilage is lined upon its upper surface by a synovia! membrane, 

 which forms a duplicature between the radius and ulna, and is called 

 the membrana sacciformis. By its lower surface it enters into the ar- 

 ticulation of the wrist-joint. 



Actions. The movements taking place between the radius and the 

 ulna are, the rotation of the former upon the latter ; rotation forwards 

 being termed pronation, and rotation backwards supination. In these 

 movements the head of the radius turns upon its own axis, within the 

 orbicular ligament and the lesser sigmoid notch of the ulna ; while 

 inferiorly the radius presents a concavity which moves upon the 

 rounded head of the ulna. The movements of the radius are chiefly 

 limited by the anterior and posterior inferior ligaments, hence these 

 are not unfrequently ruptured in great muscular efforts. 



7. Wrist Joint. The wrist is a ginglymoid articulation ; the arti- 

 cular surfaces entering into its formation being the radius and under 

 surface of the triangular fibro-cartilage above, and the rounded surfaces 

 of the scaphoid, semilunar, and cuneiform bone below ; its ligaments 

 axe four in number, 



Anterior, Internal lateral, 



Posterior, External lateral. 



The anterior ligament is a broad and membranous layer consisting 

 of three fasciculi, which pass between the lower part of the radius, and 

 the scaphoid, semilunar, and cuneiform bone. 



The posterior ligament, also thin and loose, passes between the 

 posterior surface of the radius, and the posterior surface of the semilunar 

 and cuneiform bone. 



The internal lateral ligament extends from the styloid process of the 

 ulna to the cuneiform and pisiform bone. 



The external lateral ligament is attached by one extremity to the 

 styloid process of the radius, and by the other to the side of the sea- 



