1506 



WRIST-JOINT (NORMAL ANATOMY). 



direction the tendon of the extensor secundi 

 internodii pollicis. The remainder of the 

 dorsal aspect of the radius is subjacent to the 

 tendons of the m. extensor digitorum com- 

 munis and the extensor indicis. The outer 

 surface of the lower extremity of the radius is 

 the least extensive, and is furnished with a 

 shallow groove, which affords insertion to the 

 tendon of the supinator longus, and gives 

 passage to the tendons of two of the extensor 

 muscles of the thumb, viz., the extensor ossis 

 nietacarpi pollicis and extensor primi inter- 

 nodii pollicis. This surface is terminated 

 interiorly by the sfyloid process, which lies on 

 a plane a littie posterior to the last-mentioned 

 groove : lastly, the inner surface of this por- 

 tion of the bone presents a smooth concave 

 surface of oval form, its long axis directed 

 from before backwards, which serves for arti- 

 culation witli the head of the ulna, and enters 

 into the formation of the inferior radio-ulnar 

 articulation. Bv its inferior surface, the radius 

 is adapted for articulation with the carpus. The 

 aspect of the surface, owing to the curvature 

 of the radius already indicated, is downwards 

 and forwards, whilst at the same time it is 

 directed slightly inwards, from its external 

 boundary passing lower than the internal. 



The inferior surface of the radius presents 

 a triangular outline, the apex of which is 

 placed externally at the stUoid process, whilst 

 the base, in the opposite direction, is consti- 

 tuted by the sharp margin separating the 

 inferior from the internal articular surface on 

 the radius, and serving for the attachment of 

 the broad extremity of the radio-ulnar inter- 

 articular cartilage (triangular fibro cartilage). 

 The two margins which border this inferior 

 articulating surface of the radius serve for the 

 attachment of ligaments, and of these the 

 anterior is the most prominent. Lastly, the 

 carpal surface of the radius is divided into 

 two portions by a ridge, which traverses it 

 from before backwards : the external of these 

 articular " facettes " is triangular in shape, 

 and adapted to the scaphoid bone, whilst 

 the more internal of the two is quadrilateral, 

 and articulates with the semilunar carpal bone. 



It has been mentioned that the radius at 

 its lower extremity undergoes a change of 

 form, and that from being cylindrical higher 

 up, it becomes here quadrilateral. This ex- 

 pansion of its surface takes place at the 

 expense of its solidity, for a section of the 

 bone shows that inferiority the compact tissue 

 is extremely thin, whilst the cancellated tissue 

 is in proportion more abundant. 



This circumstance is adduced, as in some 

 measure explaining the frequency of fracture 

 in this situation, an accident notoriously 

 common. 



The ulna is excluded from the articulation 

 of the wrist by the triangular fibro-cartilage, 

 which stretches across transversely between 

 the head of the ulna above and the carpus 

 ini'eriorly, and presents a surface concave in 

 each direction. 



The inferior surface of this fibro-cartilage 

 is on the same plane with the inferior surface 



of the radius, and constitutes with it the 

 superior articulating surface of the wrist-joint. 

 The entire of this conjoint surface is some- 

 what oval (or diamond-shaped), and is limited 

 externally and internally by the styloid pro- 

 cesses of the radius and ulna respectively. 



b. The Scaphoid, Semilunar, and Cuneiform 

 Hones of the Carpus. The Carpus, superiorly, 

 presents a surface which is pretty uniformly 

 convex. - That convexity, however, is slightly 

 interrupted by the undulating lines resulting 

 from the lateral articulations between the 

 bones which compose it. 



The convexity of the upper surface of the 

 scaphoid bone is triangular in form, and articu- 

 lates with the outer facette on the inferior 

 surface of the radius; the semilunar bone is 

 quadrilateral in conformity with the shape of 

 the inner facette of the radius, whilst the 

 cuneiform bone presents a surface of a trian- 

 gular form, by which it comes accura'ely into 

 apposition with the inferior surface of the 

 radio-ulnar interarticular cartilage. The aspect 

 of the radial or upper conjoint surface of 

 those three bones is directed upwards and 

 slightly backwards. 



II. Tli e Ligaments. These are placed on 

 each of the several aspects of the wrist, and 

 are usually designated from their position, 

 the anterior, the posterior, and the lateral 

 radio-carpal ligaments. But whilst the wrist- 

 joint is thus protected on its different aspects 

 by ligamentous bands, it is to be observed 

 that no distinct intervals naturally separate 

 these ligaments from one another, so that it 

 might with strict propriety be said that the 

 articulation of the wrist is defended by a 

 ligamentous envelope of a capsular form, 

 strengthened in particular parts, but more 

 especially laterally by other superimposed and 

 superadded fibres. 



a. Anterior Radio-carpal Ligament. The 

 fibres of this ligament are connected superiorly 

 to the anterior margin of the lower end of the 

 radius and of its styloid process, and to the 

 " triangular ligament," from whence they 

 radiate to their insertion into the anterior 

 surfaces of the scaphoid, semilunar, and cunei- 

 form bones. Below, they are partly con- 

 tinuous with the fibrous fasciculi (interosseous 

 ligament}, which connect the two rows of 

 carpal bones. 



The fibres of the anterior radio-carpal 

 ligament pursue a direction for the most part 

 downwards and inwards. 



By its anterior surface this ligament is in 

 relation with the tendons of the deep flexor 

 muscles, and also (but more remotely), with 

 those of the superficial flexor, and with the 

 median nerve, the entire surrounded by an 

 extensive and complicated synovial apparatus. 

 Beneath these structures, and immediately in 

 front of the ligament, is the anastomosis, 

 between the anterior radial and the anterior 

 ulnar carpal arteries, which also receive tribu- 

 taries from the descending branches of the 

 interosseal, and the ascending of the deep 

 palmar arch of arteries. 



b. 1'osffrior Radio-carpal Ligament.. This 



