METACARPAL BONE AND FIRST PHALANX. 



301 



carpal articulation may be seen by cutting through the rest of the liga- 

 ments on the posterior aspect of the hand. 



Articular surfaces. The metacarpal bone of the fore finger presents a 

 hollowed articular surface, which receives the prominence of the os tra- 

 pezoides, and articulates laterally with the os trapezium and os magnum. 

 The middle finger metacarpal articulates with the os magnum. The 

 metacarpal bone of the ring finger touches the unciform bone and the os 

 magnum. And the little finger bone is opposed to the os unciforme. 



Synovia! membranes. Usually two synovial membranes are interposed 

 between the carpal and metacarpal bones, viz., a separate one for the bone 

 of the thumb, and offsets of the common carpal synovial sac (p. 299) for 

 the others. Sometimes there is a distinct synovial sac for the articulation 

 of the os unciforme with the two inner metacarpals. 



Interosseous ligaments. The interosseous ligaments between the bases 

 of the metacarpal bones may be demonstrated by detaching one bone from 

 another. There are also strong fibrous pieces between all the carpal bones 

 in the second row ; and slight ones are described as present on each side 

 of the os semilunare in the first row. 



Dissection. For the examination of the joint between the head of the 

 metacarpal bone and the first phalanx of the finger, it will be requisite to 

 clear away the tendons and the tendinous expansion around it. A lateral 

 ligament on each side, and an anterior thick band are to be defined. One 

 of the joints may be opened to see the articular surfaces. 



The same dissection may be made for the articulations between the pha- 

 langes of the finger. 



UNION OF METACARPAL BONE AND FIRST PHALANX (fig. 96). In 

 this joint the convex head of the metacarpal bone is received into the 

 glenoid fossa of the phalanx, and the two 

 are retained in contact by the extensor and 

 flexor tendons, and by the following liga- 

 ments : 



The lateral ligament (a) is the same on 

 both sides of the joint. P^ach is triangular 

 in form : it is attached by its upper part to 

 the tubercle on the side of the head of the 

 metacarpal bone, and below it is inserted into 

 the side of the phalanx and the anterior 

 ligament. 



The anterior ligament (&) is a longitu- 

 dinal band, which is fixed firmly to the 

 phalanx, but loosely to the metacarpal 

 bone. It is fibro-cartilaginous in texture, 



and is grooved for the flexor tendon : to its sides the lateral ligaments are 

 attached. 



Covering the upper part of the joint is the extensor tendon ; this takes 

 the place of a dorsal ligament, and sends down an expansion on each side 

 which serves as a capsule to the articulation. The synovial membrane of 

 the joint is a simple sac. 



In the articulation of the thumb two sesamoid bones are connected with 

 the anterior ligament, and receive most of the fibres of the lateral liga- 

 ments. 



Movements. Motion in four opposite directions, and circumduction, exist 

 in these condyloid joints. 



Fig. 96. 



