BONES OF THE HAND. 



509 



with the cuneiform bone demands a separate 

 consideration. A plane oval surface on the 

 posterior part of the pisiform is articulated 

 with a corresponding one on the palmar aspect 

 of- the cuneiform, and several strong ligaments 

 strengthen the joint. Two lateral ligaments 

 pass from the pisiform to the cuneiform bone, 

 the internal, which is also anterior, being of 

 considerable strength. This bone is further 

 connected to the unciform by strong ligament- 

 ous fibres; and a strong bundle, which bears the 

 same relation to the tendon of the flexor carpi 

 ulnaris as the ligamentum patellae does to the 

 tendon of the rectus fernoris, extends to the 

 carpal extremity of the fifth metacarpal bone. 

 This joint is provided with a loose synovial 

 membrane; its motions are those of gliding 

 in the directions of the axis of the articular 

 surfaces. 



Carpo-metacarpal joints. These are very 

 strong articulations, and, with the exception of 

 the first and fifth, enjoy a very limited extent 

 of motion. The four internal ones are nearly 

 planiform arthrodise, restricted on the palmar 

 and dorsal surfaces by strong and short liga- 

 ments (palmar and dorsal ligaments), the latter 

 being much better developed. The second 

 metacarpal bone is articulated with the trapezoid 

 in an extremely firm manner: its palmar liga- 

 ment extends from the extremity of the meta- 

 carpal bone to the trapezium internal to the 

 ridge, and covered by the tendon of the radial 

 flexor of the wrist. There are three dorsal 

 ligaments, an external attached to the trapezium, 

 and an internal to the os magnum. These two 

 ligaments are oblique in their direction ; the 

 third or middle one is vertical and attached to 

 the trapezoid. The third metacarpal bone is arti- 

 culated with the os magnum : here we find 

 three strong palmar ligaments, an external one 

 which extends obliquely outwards to the trape- 

 zium, an internal one which passes in front of 

 the carpal extremity of the fourth metacarpal 

 bone, adhering to it, and inserted into the 

 unciform and the fifth metacarpal bone, and a 

 middle one which passes vertically to the os 

 magnum. This joint has two dorsal ligaments, 

 both inserted into the os magnum. The fourth 

 metacarpal bone is articulated with the radial 

 portion of the inferior articular surface, and 

 with a very small portion of the os magnum ; 

 it has a single palmar and dorsal ligament. 

 The fifth metacarpal bone is articulated with 

 the outer part of the inferior surface of the 

 unciform; this surface is convex transversely 

 and concave from before backwards, while that 

 on the metacarpal bone is convex from before 

 backwards and concave transversely. The 

 proper ligaments of this joint are very feeble, 

 being merely a few fibres attached to the ante- 

 rior and posterior surfaces of the synovial mem- 

 brane. The joint, however, is protected in 

 front by the prominence of the unciform pro- 

 cess, which descends a little below the line of 

 the articulation, and limits the forward motion 

 of the carpal extremity of the bone ; and pos- 

 teriorly it is strengthened by the tendon of the 

 extensor carpi ulnaris, while its motion ulnad 

 is restricted by the strong internal palmar liga- 



ment of the third metacarpal bone, which we 

 have already described as passing from that 

 bone to the fifth metacarpal and the unciform 

 bones. The fifth carpo-metacarpal articulation 

 approaches in many particulars to the first; it 

 has a greater latitude of motion than the three 

 immediately preceding it, and its articular sur- 

 faces very much resemble those of the first. 



Besides the palmar and dorsal ligaments 

 already described, these metarcarpal bones are 

 very firmly connected to each other by short 

 but strong ligaments, extending transversely 

 from one to the other on the palmar and dorsal 

 aspects. 



A common synovial membrane extends 

 throughout the four joints above described ; 

 this synovial membrane is continuous with that 

 between the two rows of carpal bones. 



The digital extremities of the four inner 

 metacarpal bones are connected by their trans- 

 verse ligaments situated at the palmar surface 

 and extending from one to the other. 



Carpo-metacarpal joints of the thumb. The 

 main feature by which this articulation is dis- 

 tinguished from the other carpo-metacarpal 

 joints is its great mobility. It is an arthrodia, 

 and in many particulars resembles very much 

 the sterno-clavicular joint. The trapezium 

 presents a surface concave from within out- 

 wards, and convex from before backwards, 

 that on the metacarpal bone being convex in 

 the transverse, and concave in the antero-pos- 

 terior direction. 



The ligamentous apparatus of this joint has 

 very much the appearance of the capsular 

 ligament of an enarthrosis, and has indeed 

 been described as such by many anatomists ; 

 but on a careful examination it will be found 

 to consist of separate bundles of ligament 

 placed at those situations in which the greatest 

 tendency to displacement exists in the various 

 motions of the joint. Four principal bundles 

 may be described : one very thick and strong, 

 situated at the posterior and outer part of the 

 joint, (lig. dorsale, Weitbr.) extending from 

 the metacarpal bone to a prominent tubercle 

 on the outer part of the dorsal surface of the 

 trapezium; this ligament limits flexion of the 

 joint. A second ligament is situated directly 

 in front of the joint, (lig. palmare, Weitbr.) 

 is inserted into the trapezium immediately 

 internal to its prominence; extension is limited 

 by this ligament. The third and fourth bundles 

 (Lig. laterale ext. et int. Weitbr.) are situ- 

 ated on the radial and ulnar sides of the joint : 

 they are less distinct as well as less strong than 

 those last described. That on the ulnar side 

 is considerably the stronger; it limits abduc- 

 tion of the thumb, whilst that on the radial 

 side limits adduction. 



The synovial membrane of this joint is lax ; 

 it is perfectly distinct from the general syno- 

 vial membrane of the other carpo-metacarpal 

 articulations. 



Motions of the carpo-metacarpal joints. 

 In the second, third, and fourth joints the 

 motions are limited to a very slight, and during 

 life scarcely appreciable gliding forwards or 

 backwards: the strong transverse ligaments, 



