LIGAMENTS OF WRIST JOINT. 



297 



Fig. 93. 



Flexion and extension. In flexion the hand is moved forwards and in- 

 wards, whilst the carpus rolls on the radius from before back, and projects 

 behind, stretching the posterior ligament. In extension the hand is car- 

 ried backwards and outwards, and the row of carpal bones moves in the 

 opposite direction, viz., from behind forwards, so as to cause the anterior 

 ligament to be tightened. The hinder movement is freer than the forward. 



Abduction and adduction. The row of carpal bones moves transversely 

 inwards in the former, and outwards in the latter state ; and the move- 

 ment is freer towards the ulnar than the radial side. 



The latter ligaments are put on the stretch, the inner in abduction and 

 the outer in adduction ; and the motion is limited on the outer side by 

 the meeting of the styloid processes of the radius with the scaphoid bone. 



Circumduction. The hand describes a cone in this movement, whose 

 apex is at the wrist and base at the digits ; and it moves more freely in 

 extension and adduction than in the opposite directions. 



LOWER RADIO-ULNAR ARTICULATION. In this articulation the con- 

 vexity of the end of the ulna is received into a concavity on the radius ; 

 an arrangement just the opposite to that be- 

 tween the upper ends of the bones. 



The chief bond of union between the 

 bones is a strong fibro-cartilage ; but a kind 

 of capsule consisting of scattered fibres, sur- 

 rounds loosely the end of the ulna. 



The triangular Jibro-cartilage (fig. 93, c) 

 is placed transversely beneath the end of the 

 ulna, and is thickest at its margins and apex. 

 By its base the cartilage is fixed to the ridge 

 which separates the carpal from the ulnar 

 articulating surface of the radius ; and by its 

 apex to the styloid process of the ulna, and 

 the depression at the root of that point of 

 bone. Its margins are united with the con- 

 tiguous anterior and posterior ligaments of 

 the wrist joint ; and its surfaces enter into 

 different joints, viz., the wrist, and the lower 

 radio-ulnar. It serves to unite the radius 

 and ulna, and to form part of the socket for the carpal bones, 

 ally it is perforated by an aperture. 



The synovia! membrane (membrana sacciformis) is very loose, from 

 which circumstance it has received its name, and ascends between the 

 radius and the ulna : it is separated from that of the wrist-joint by the 

 triangular fibro-cartilage. 



The use of this articulation is referred to with the movements of the 

 radius (p. 295). 



UNION OF THE CARPAL BONES. The several bones of the carpus are 

 united into two rows by dorsal, palmar, and interosseous bands : and the 

 two rows are connected to each other by separate ligaments. 



Dissection. The articulation of the carpal bones with each other will 

 be prepared by taking away all the tendons from the hand, and claming 

 carefully the whole of the connecting ligamentous bands. Two distinct 

 ligaments of the pisiform bone to the unciform and fifth metacarpal are 

 to be defined in the palm. 



THE WRIST JOINT OPENED TO SHOW 

 THE ARCH FORMED BY THE BONES 

 OF THE FOREARM WITH THE UNIT- 

 ING FlBKO-CARTILAGE, C. 



a. Radius. 



6. Ulna. 



Occasion- 



