272 THE ARTICULATIONS 



8. THE CARPO-METACARPAL JOINTS 

 These may be divided into two sets, namely: — 



(a) The carpo-metacarpal joints of the four medial fingers. 

 (6) The carpo-metacarpal joints of the thumb. 



The inferior surfaces of the bones of the second row of the carpus present a 

 composite surface for the four medial metacarpal bones; the greater multangular 

 presents in addition a distinct and separate saddle-shaped surface for the base of 

 the metacarpal bone of the thumb. 



(a) The Four Medial Carpo-metacarpal Joints 



Class. — Diarthrosis. Subdivision. — Arthrodia. 



These joints exist between the greater and lesser multangular, capitate, and 

 hamate bones above, and the four medial metacarpal bones below. The liga- 

 ments which unite them are, dorsal, volar, and interosseous. 



The dorsal ligaments (fig. 303). — Three dorsal ligaments pass to the second metacarpal 

 bone: one from each of the carpal bones with which it articulates, viz., the greater and lesser 

 multangular, and capitate. Two dorsal bands pass from the capitate to the third metacarpal 

 bone. Two dorsal bands pass to the foiu-th bone: viz., one from the hamate, and another from 

 the capitate; the latter is sometimes wanting. The fifth bone has only one band passing to it 

 from the hamate. 



The volar ligaments (fig. 300). — One strong band passes from the second metacarpal bone 

 to the greater multangular medial to the ridge for the transverse carpal hgament; it is covered 

 by the sheath of the flexor carpi radialis. 



Three bands pass from the third metacarpal: one laterally to the greater multangular, a 

 middle one upward to the capitate, and a third medially over the fourth to reach the fifth meta- 

 carpal and the hamate bones. 



One ligament connects the fourth bone to the hamate. 



One ligament connects the fifth bone to the hamate, the fibres extending medially, and con- 

 necting the dorsal and volar ligaments. The ligament to the fifth bone is strengthened in front 

 by the prolonged fibres of the flexor carpi ulnaris and the strong medial sUp of the ligament of 

 the third metacarpal bone; and posteriorly, by the tendon of the extensor carpi ulnaris. 



The interosseous ligament (fig. 304) is limited to one part of the articulation, and consists 

 of short fibres connecting the contiguous angles of the hamate and capitate with the third and 

 fourth metacarpal bones toward their volar aspect. There is, however, a thick strong ligament, 

 connecting the edge of the greater multangular with the lateral border of the base of the second 

 metacarpal bone; it helps to separate the carpo-metacarpal joint of the thumb from the common 

 carpo-metacarpal joint, and to close in the radial side of the latter joint. 



The synovial membrane is a continuation of the medio-carpal joint; occasionally there is 

 a separate membrane between the hamate and fourth and fifth metacarpal bones (fig. 304); 

 while that between the fourth and capitate is lined by the synovial sac of the common joint. 



The arteries to the four medial carpo-metacarpal joints are as foUows: — 



(1) For the index finger: twigs are supplied by the trunk of the radial on the dorsal and volar 

 aspects, and by the dorsal and volar metacarpal branches. 



(2) For the middle finger: the first dorsal metacarpal by the branch which passes upward 

 to join the dorsal carpal arch, and a branch from the deep volar arch which joins the volar carpal 

 arch. 



(3) For the ring finger: the deep volar arch and recurrent twigs from the second dorsal 

 metacarpal in the same manner as for the middle finger. 



(4) For the little finger: the ulnar and its deep branch; also twigs from the second dorsal 

 metacarpal. 



The nerves are supplied to these joints by the deep volar branch of the ulnar, the deep branch 

 of the raflial (posterior interosseous), and the median. 



Relations. — In front of the four medial carpo-metacarpal joints are the flexors of the 

 fingers with their synovial sheath. The flexor carpi radialis crossing in front of the lateral part 

 of the joint and the fibres of the oblique adductor poUicis which spring from the capitate and 

 lesser multangular are also anterior relations. Behind the joints are the extensors of the wrist 

 and fingers with their synovial sheaths and the dorsal metacarpal arteries. At the lateral border 

 of the joints between the index and lesser multangular lies the radial artery. 



The movements permitted at these joints, though slight, serve to increase those of the 

 medio-carpal and wri.st-joints. "^I'he joint between the fifth metacarpal and the hamate bones 

 approachoH soniewhat in shape and luobility the first carpo-metacarpal joint; it has a greater 

 range of flexion and extension, but its side to side movement is nearly as limited as that of the 

 three other metacarpal hones; the process of the hamate bone limits its flexion. Motion toward 

 the ulnar side is checked by the strong palmar band which unites the base of the fifth meta- 

 carpal to the bft.se of the tliird, and the strong transverse ligament at the head of the bonee. 

 The mobility of the second, third, and fourth metacarpal bones is very limited, and consists 

 almost entirely of a slight gliding upon the carpal bones, i. e., flexion and extension; that of the 

 third and fourth bones is extremely slight, as there is no long flexor attached to either; but, 



