244 



THE ARTICULATIONS 



The nerves are derived from tlie digital branches, or from twigs of the branches 

 of the uhiar to the interosseous muscles. 



The movements permitted at these Joints are: flexion, extension, abduction, 

 adduction, and circumduction. Flexion is the most free of all, and may be con- 

 tinued until the jihalanx is at a right angle with the metacarpal bone. It is on this 

 account that the articular surface of the head of the bone is prolonged so much 

 furtlier on the palmar aspect, and that the synovial sac is here so loose and ample. 

 Extension is the most limited of the movements, and can only be carried to a little 

 beyond the straiglit line. Abduction and adduction are fairly free, V»ut not so free 

 as flexion. Flexion is associated with adduction, and extension with abduc- 

 tion. This may be proved by opening the hand, when the fingers involuntarily 

 separate as they extend, while in closing the fist they come together again. The 

 free abduction, adduction, and circumduction which are permitted at these joints 

 are due to the fact that the long axes of the articular facets are at right angles 

 to one another. 



Fig. 236. — .Anterior and Posteeiok View of Ligaments of the Fingers. 



Transverse ligament 

 between the heads 

 of the metacarpal 

 bones 



Glenoid ligament 

 \\ — Lateral ligament 



Areolar tissue 

 capsule 



Lateral ligament 



Glenoid ligament 

 Lateral ligament 



Flexor tendon 



Areolar tissue 

 capsule 

 Lateral ligament 



Extensor tendon 



Flexor tendon 



Slips of the extensor . 

 tendon 



(h) The Metacarpo-phalangeal Joint of the Thumb 

 Class. — Diarthrosis. Subdivision. — Condylarthrosis. 



The head of the metacarpal lione of the thumb differs consideral)ly from the 

 corresponding ends of the metacarpal bones of the fingers. It is less convex, wider 

 from side to side, the ])almar edge of the articular surface is raised and irregular, 

 and here on eitJKM- side of the median line are the two facets for the sesamoid bones. 

 The base of the first jthalanx of the thumb, too, is more like the base of the second 

 phalanx of one of the other fingers. The ligaments are: — 



Lateral. Posterior. 



Sesamoid bones in place of a glenoid ligament. 



