1 64 THE UPPER EXTREMITY 



of the phalanx, but only slightly connected with the meta- 

 carpal bone. Occupying the interval between the two col- 

 lateral ligaments it is united to both by its margins, so that 

 the three ligaments are more or less directly continuous. 



The volar accessory ligament also exhibits a close 

 connection with the transverse ligament of the heads of the 

 metacarpal bones which stretches transversely across the heads 

 of the metacarpal bones, and its volar surface is grooved 

 for the flexor tendons as they proceed distally over the 

 joint. Further, the fibrous sheath, which bridges over the 

 tendons, is fixed to its borders. 



Ligg. Collateralia (O.T. Lateral Ligaments). The col- 

 lateral ligaments are placed one on either side of the joint. 

 Each is a strong, thick, and short band, which is attached, 

 on the one hand, to the tubercle and depression on the 

 corresponding side of the head of the metacarpal bone, and 

 on the other to the base of the phalanx and the border of the 

 volar ligament. 



Dissection. The extensor tendon should now be raised from the dorsal 

 aspect of the joint. By this proceeding the joint is opened, and a 

 demonstration is afforded of the fact that the metacarpo-phalangeal joints 

 are only represented dorsally by the stratum synoviale. 



Stratum Synoviale (Synovial Membrane). A synovial 

 membrane lines the deep surfaces of the capsula articularis 

 in each joint, and also the deep surface of the extensor 

 tendon, as it passes over the articulation. The tendon there- 

 fore takes the place of the stratum fibrosum of the capsule. 



Movements at the Metacarpo-phalangeal Joints. The movements of 

 the first phalanx at these joints are (a) flexion^ or volar movement ; 

 (b) extension, or dorsal movement ; (c) abduction ; and (d) adduction. 



During flexion of the fingers the first phalanx travels volarwards with 

 the thick accessory volar ligament upon the head of the metacarpal 

 bone. The interosseous and lumbrical muscles are chiefly instrumental 

 in producing this movement. 



The first phalanges of the fingers in the movement of extension can 

 only be carried dorsally to a very slight degree beyond the line of the 

 metacarpal bones. The extensor conwmnis and the special extensors of the 

 index and little finger are the muscles which operate in this case. 



Abduction and adduction are movements of the first phalanx away from 

 and towards a line prolonged distally through the middle finger, and 

 are seen when the fingers are spread out and again drawn together. The 

 abductor digiti quinti and the dorsal interosseous muscles act as abductors 

 of the fingers at these joints, whilst the volar interosseous muscles operate 

 as adductors of the little, ring, and index fingers. In the case of 

 the middle digit, the second and third dorsal interosseous muscles act 

 alternately as abductors and as adductors. In connection with the 



