THE METACARPO-PHALAXGEAL JOINTS 243 



bone to bone; they cannot l)e well differentiated from the other ligaments and 

 fil)rous tissue eoverinw; the 1 tones. 



The interosseous ligaments (fig. 23o) pass between the apposed surfaces of 

 the bones, and are attached to the distal sides of the articular facets, so as to close 

 in the synovial cavities on this aspect; where there are two articular facets, the 

 fibres extend upwards lietween them, nearly as far as their carpal facets. That 

 between the fourth and fifth is the weakest. 



The arteries to the intermetacarpal joints are twigs from the palmar and dorsal 

 interosseous arteries; the twigs pass upwards between the interosseous muscles. 



The nerves are derived from the ulnar and the posterior interosseous. 



The synovial membrane is prolonged downwards from the common carpal sac. 



The Union of the Heads of the Metacarpal Bones 



The distal extremities of these bones are connected together on their palmar 

 aspects by what is called the transverse ligament. This consists of three short 

 bands of fibrous tissue, which unite the second and third, third and fourth, and the 

 fourth and fifth bones. They are rather more than a quarter of an inch (6 mm.) 

 deep, and rather less in width, and limit the distance to which the metacarpal bones 

 can be separated. They are continuous above with the fascia covering the inter- 

 osseous muscles; below, they are connected with the subcutaneous tissue of the 

 Aveb of the hand. They are on a level with the front surfaces of the bones, and are 

 l)lended on either side with the edges of the glenoid ligament in front, with the 

 lateral ligaments of the metacarpo-phalangeal joint, and also with the sheaths of 

 the tendons. In front, a lumbrkal muscle passes with the digital artenes and 

 nerves; while behind, the interossei muscles pass to their insertions. 



10. THE METACARPO-PHALANGEAL .JOINTS 



(a) The ]Metacarpo-phalangeal Joints of the Four Inner Fingers 



Class. — Diarthrosis. Subdivision. — Condylaiihrosis. 



In these joints the cup-shaped extremity of the base of the first phalanx fits 

 on to the rounded head of the metacarpal bone, and is united by the following 

 ligaments: — 



Lateral. Glenoid. 



The glenoid ligament (fig. 236) is a fibro-cartilaginous plate which seems more 

 intended to increase the depth of the phalangeal articular facet in front, than to 

 unite the two bones. It is much more firmly attached to the margin of the phalanx 

 than to the metacarpal bone, being only loosely connected with the palmar surface 

 of the latter by some loose areolar tissue which covers in the synovial sac, here 

 prolonged upon the surface of the bone some little distance. Laterally, it is 

 connected with the lateral ligaments and the transverse metacarpal ligament. It 

 corresponds to the sesamoid bones of the thumb; a sesamoid bone sometimes exists 

 at the inner border of the joint of the little finger. 



The lateral ligaments (figs. 235 and 236) are strong and firmly connect the bones 

 with one anotlier; each is attached above to the lateral tubercle, and to a depression 

 in front of the tubercle, of the metacarpal bone. From this i)oint the fibres spread 

 widely as they descend on the side of the base of the ])halanx; the anterior fibres 

 are connected with the glenoid ligament; the posterior blend with the tendinous 

 expansion at the l>ack of the joint. 



The joint is covered in posteriorly by the expansion of the extensor tendon, and 

 some loose areolar tissue passing from its under surface to the bones (fig. 236). 



The synovial sac is loose and capacious, more especially over the base of the 

 phalanx behind, and tlie head of the metacarpal bone in front. 



The arteries come from the digital or anterior interosseous vessels of the deep 

 arch. 



