JOINTS OF PHALANGES. 



105 



extending 



lateral 

 motion ; 



The anterior ligament (6) is a strong and dense band, which is anterior 

 fixed firmly to the phalanx, but loosely to the metacarpal bone. lgan 

 It is grooved for the flexor tendon ; and to its sides the lateral 

 ligaments are united. 



On the dorsal aspect of the joint, the capsule is completed by posterior, 

 a thin layer of connective tissue which supports the synovial 

 membrane, and is closely covered by the extensor tendon. The 

 synovial membrane of the joint is a simple sac. Synovial 



In the articulation of the thumb two sesamoid bones are con- Joint of 

 nected with the anterior ligament, and receive most of the fibres of thumb, 

 the lateral ligaments. 



Movements. Motion in four opposite directions, together with Kinds of 

 circumduction, take place in these condyloid joints. 



Flexion and extension. Inflexion, the phalanx glides forwards bending ; 

 over the head of the metacarpal bone, a"nd 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. In 

 extension the anterior ligament and 

 the flexor tendons are stretched, and 

 limit the movement. 



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 

 rendered convex is tightened, and 

 the other is relaxed. 



The circumductory motion is less 

 impeded in the fore and little 

 fingers than in the others. In the joint of the thumb the movements, 

 especially to the side, are much less extensive than in the fingers. 



UNION OF THE PHALANGES. The ligaments of these joints are joints of the 

 similar to those in the metacarpo-phalangeal articulations, viz., two {lave 8 " 86 "* 

 lateral, an anterior and a membranous posterior. 



The lateral ligaments are triangular in form. Each is connected lateral and 

 by its apex to the proximal phalanx at the side of the head ; and 

 by its base to the distal phalanx and the anterior ligament. 



The anterior ligament has the same mode of attachment between anterior 

 the extremities of the bones as in the metacarpo-phalangeal joint, llgan 

 but it is not so strong. 



There is a simple synovial membrane present in the joint. Synovial 



The joint of the second with the last phalanx is like the pre- sac- 

 ceding in the number and disposition of its ligaments ; but all the Last < ' omt ' 

 articular bands are much less strongly marked. 



Articular surfaces. The head of each phalanx is marked by a Surfaces of 

 pulley-like surface. The base presents a hollow on each side of a the bones - 

 median ridge, which fits into the central depression of the opposed 

 articular surface. 



FIG. 45. 



circumduc- 

 tory. 



