THE CARPO-METACARPAL JOINTS 241 



(a) The Four Inner Carpo-metacarpal Joints 

 Class . — Dia rtJi /-o^/.i'. Subdivision . — Arth roduL . 



These joints exist between the trapezium, trapezoid, magnum, and unciform 

 1 tones above, and tlie four inner metacarpal bones below. The ligaments Avhich 

 unite them are, dorsal, palmar, and interosseous. 



The dorsal ligaments (fig. 234). — Three dorsal ligaments pass to the second 

 metacari»al l»one: one from each of the carpal l)ones with which it articulates, 

 viz. the trapezium, trapezoid, and magnum. Two dorsal bands pass from the 

 magnum to the third metacarpal bone. Tavo dorsal bands pass to the fourth bone : 

 viz. one from the unciform, and another from the magnum; the latter is sometimes 

 wanting. The fifth l)one has only one band passing to it from the unciform. 



The palmar ligaments (fig. 231). — One strong band passes from the second 

 metacarpal bone to the trapezium internal to the ridge for the annular ligament; it 

 is covered by the sheath of \\\ii flexor carpi radialis. 



Three bands pass from the third metacarpal: one outwards to the trapezium, a 

 middle one upwards to the magnum, and a third inwards over the fourth to reach 

 the fifth metacarpal and the unciform bones. 



One ligament connects the fourth bone to the unciform. 



One ligament connects the fifth bone to the unciform, the fibres extending 

 internally, and connecting the dorsal and palmar ligaments. The ligament to the 

 fifth l)one is strengthened in front by the prolonged fil^res of the flexor carpi ulnaris 

 and the strong inner slip of the ligament of the third metacarpal Ijone; and poste- 

 riorly, by the tendon of the extensor carpi tdnaris. 



The interosseous ligament (fig. 235) is limited to onej)artof the articulation, 

 and consists of short strong fibres connecting the contiguous angles of the unciform 

 and magnum with the third and fourth metacarpal bones towards their palmar 

 aspect. There is, however, a thick strong ligament connecting the edge of the 

 trapezium with the outer border of the base of the second metacarpal ])one; it helps 

 to separate the carpo-metacarpal joint of the thumb from the common carpo-meta- 

 (•ar])al joint, and to close in the radial side of the latter joint. 



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

 sionally there is a separate membrane between the unciform and fourth and fifth 

 metacarpal bones (fig. 235); while that between the fourth and magnum is lined 

 by the synovial sac of the common joint. 



The arteries to the four inner carpo-metacarpal joints are as follows: — 



(1) Fur the index finger: twigs, are suppliecl by the trunk. of the radial on the 

 dorsal and palmar aspects, the metacarpal, the dorsalis indicis, and the radialis 

 indicis. 



(2) For the middle finger: the metacarpal, first dorsal interosseous by the 

 V)ranch which passes upwards to join the posterior carpal arch, and a branch from 

 the deep palmar arch which joins the anterior carpal arch. 



(3) For the ring finger: the deep palmar arch and recurrent tAvigs from the 

 second dorsal interosseous 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 interosseous. 



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

 the posterior interosseous, and the median. 



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

 of the medio-cari^al and wrist-joints. The joint between the fifth metacarpal and 

 the unciform bones approaches somewhat in shape and mobility the first carpo- 

 metacarpal joint; it has a greater range of flexion and extension, but its lateral 

 movement is nearly as limited as that of the three other metacarpal bones; the 

 process of the unciform bone limits its flexion. Lateral motion towards the ulnar 

 side is checked by the strong palmar liand which unites the base of the fifth 

 metacarpal to the base of the third, and the strong transverse ligament at the head 

 of the bones. 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 

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