METACARPO-PHALANGEAL JOINTS. 



333 



The synovial stratum (Fig. 311) is usually single and lines the fibrous stratum, 

 but, as already explained, it has prolongations into the intermetacarpal and inter- 

 carpal series of joints. In connexion with the intercarpal series, the frequent 

 absence of the interosseous ligament between the greater and lesser multangular 

 bones permits the free communication of this joint cavity with that of the 

 transverse carpal joint. 



ARTICULATIONES METACARPOPHALANGE^E. 



Metacarpo-phalangeal Joints. In the case of the pollex this joint is con- 

 structed on the plan of a ginglymus diarthrosis; the four corresponding joints 

 of the fingers are also diarthroses of a slightly modified ball-and-socket variety. 

 With the exception of the metacarpal bone of the pollex, 

 each metacarpal bone has a somewhat spherical head 

 articulating with a shallow oval cup upon the base of the 

 first phalanx. It is important to note that the articular 

 surface upon the head of each of these metacarpal bones 

 is wider on the volar aspect and narrower on the dorsal 

 aspect. The articulation in the thumb presents features 

 similar to those of an interphalangeal joint. 



Each joint possesses a capsula articularis (Fig. 312) 

 which presents very different degrees of strength in 

 different aspects of the articulation. Thus, on the dorsal 

 aspect, it cannot be demonstrated as an independent 

 structure, but the necessity for dorsal ligaments is to 

 a large extent obviated by the presence of the strong 

 flattened expansions of the extensor tendons. 



The epiphyseal lines are extra-capsular. 



Ligamenta Collateralia. The collateral ligaments 

 (O.T. internal and external lateral) (Fig. 312) are strong 

 cord-like bands which pass from the tubercles and adjacent 

 depressions on the sides of the heads of the metacarpal 

 bones to the contiguous non-articular areas on the bases 

 of the proximal phalanges. They are intimately connected 

 on their volar aspects with the volar ligaments. 



Ligamenta Accessoria Volaria. The volar accessory 

 ligaments (O.T. palmar ligaments) consist of thick plates of 

 fibro- cartilage loosely connected to the metacarpal bones, 

 but firmly adherent to the phalanges. They are placed 

 between the collateral ligaments, to both of which they 

 are in each case connected. Each plate is grooved on the 

 volar surface for the long flexor tendons, whilst on its 

 dorsal or joint surface it supports and glides upon the 

 head of the metacarpal bone during flexion and extension 

 of the joint. In the case of the thumb this plate of FlG 312 ._ METACAKPO-PHALAN- 

 fibro-cartilage is usually replaced by sesamoid bones, and 

 in the case of the index finger one such sesamoid nodule 

 is frequently found at the radial side of the plate. 



An important accessory ligament is found in connexion with the four medial 

 metacarpo-phalangeal articulations, viz. : 



Ligamenta Capitulorum (Oss. Metacarpalium) Transversa. The transverse 

 ligament of the heads of the metacarpal bones (or transverse metacarpal ligament) 

 binds together the distal extremities of the four medial metacarpal bones. The 

 name is applied to three sets of transverse fibres of great strength which are 

 situated in front of the three medial interosseous spaces. These fibres are con- 

 tinuous with the ligamenta accessoria volaria (volar metacarpo-phalangeal ligaments) 

 at their lateral margins. 



A stratum synoviale lines the capsula articularis of each joint. 



Capsule 



GEAL AND 



JOINTS. 



Collateral 

 ligament 



INTERPHALANGEAL 



