302 DISSECTION OF THE UPPER LIMB. 



Extension and flexion. The phalanx moves backwards in extension, so 

 as to give an angle with the metacarpal bone. The anterior ligament and 

 the flexor tendons are stretched, and control the movement. In flexion 

 the phalanx glides forwards under the head of the metacarpal bone, and 

 leaves this exposed to form the knuckle when the finger is shut. The 

 lateral ligaments and the extensor tendon are put on the stretch as the 

 joint is bent. 



Abduction and adduction are the lateral movements of the finger from 

 or towards the middle line of the hand. The lateral ligament of the side of 

 the joint which is convex will be tightened, and the other will be relaxed. 



The circumductory motion is less impeded in the thumb, and in the fore 

 and little fingers than in the others ; and in the thumb it allows the turn- 

 ing of the last phalanx towards the other digits in the movement of oppo- 

 sition. 



UNION OF THE PHALANGES. The ligaments of the first joint are simi- 

 lar to those in the metacarpo-phalangeal articulation, viz., two lateral and 

 an anterior. 



The lateral ligaments are triangular in form. Each is connected by its 

 apex to the side of the phalanx near the anterior part ; and by its base to 

 the contiguous phalanx and the anterior ligament. 



The anterior ligament has the same mode of attachment between the 

 extremities of the bones as in the metacarpo-phalangeal joint, but it is not 

 so strong ; and the extensor tendon takes the place of a posterior band as 

 in that articulation. 



There is a simple synovial membrane present in the joint. 



The joint of the second with the last phalanx is like the preceding in 

 the number and disposition of its ligaments ; but all the articular bands 

 are much less strongly marked. 



Articular Surfaces. The anterior end of each phalanx is marked by a 

 pulley-like surface. The posterior end presents a transversely hollowed 

 fossa, and is provided with a crest which fits into the central depression of 

 the opposed articular surface. 



Movements. The two interphalangeal joints can be bent and straight- 

 ened like a hinge. 



Flexion and extension. In flexion, the farther phalanx moves under the 

 nearer in each joint, and the motion is checked by the lateral ligaments 

 and the extensor tendon : in the joint between the middle and the meta- 

 carpal phalanx this movement is most extensive. In extension the farther 

 phalanx comes into a straight line with the nearer one and the motion is 

 stopped by the anterior ligament and the flexor tendons. 



