102 



DISSECTION OF THE UPPER LIMB. 



One synovial 

 cavity for 

 the carpal 

 bones, 



and some 

 meta- 

 carpals. 

 Kinds of 

 motion : 



flexion ; 



extension . 



Combined 

 movements 

 of radio- 

 carpal and 

 transverse 

 carpal 

 joints ; 



flexion and 

 extension ; 



abduction ; 



adduction ; 



and circum- 

 duction. 



Metacarpal 

 bones joined 

 at 



with 



synovial 



joints, 



and at 

 heads. 



making up a condyloid projection which is received into the arch 

 of the first row, and the trapezium and trapezoid forming a slight 

 hollow for the convexity of the scaphoid bone. 



One synovial sac serves for the articulation of all the carpal bones, 

 except the pisiform with the pyramidal. The cavity extends trans- 

 versely between the two rows of the carpus, and is continued 

 upwards and downwards between the individual bones. The offsets 

 upwards are two, and they sometimes open into the cavity of the 

 wrist-joint ; but the offsets in the opposite direction are three, and 

 may be continued to all, or only to the two outer of the four 

 inner carpo-metacarpal joints. 



Movements. Owing to the irregular shape of the articular 

 surfaces, only forward and backward movements are permitted in 

 the transverse carpal joint. 



Flexion. As the hand is brought forwards, the os magnum and 

 unciform move backwards in the socket formed by the first row, 

 while the trapezium and trapezoid advance over the scaphoid, and 

 the posterior ligament is tightened. 



Extension. The backward movement is freer than flexion. The 

 trapezium and trapezoid glide backwards over the scaphoid, and the 

 os magnum and unciform project on the palmar aspect, the move- 

 ment being checked by the anterior ligament of the joint and the 

 strong flexor tendons. 



The axes upon which the movements of flexion and extension of 

 the radio-carpal and transverse carpal joints take place are not 

 strictly transverse, but oblique in opposite directions, that of the 

 proximal articulation having its inner end directed forwards, while 

 that of the distal articulation is inclined from without inwards and 

 backwards. In order therefore to move the hand directly forwards 

 or backwards, both joints are called into play simultaneously. By 

 a combination of flexion in the one joint with extension in the 

 other, lateral movements (abduction and adduction) of the hand are 

 produced. Thus, abduction results from flexion of the radio-carpal 

 and extension of the transverse carpal articulation, and adduction, 

 which is the freer movement, from extension of the radio-carpal 

 and flexion of the transverse carpal joint. In circumduction the 

 hand passes successively through the several states of angular move- 

 ment, describing a cone with the apex at the wrist, and the 

 excursion is greater in the direction of flexion and adduction than 

 in the opposite directions. 



UNION OF THE METACARPAL BONES. The metacarpal bones of 

 the four fingers are connected at their bases by the following liga- 

 ments : A dorsal (fig. 44) and palmar (fig. 41) fasciculus of fibres 

 passes transversely from each bone to the next ; and the bands in 

 the palm are the strongest. Besides these, there is a short interosseous 

 ligament between the contiguous rough surfaces of the bones. 



Where the metacarpal bones touch they are covered by cartilage ; 

 and between the articular surfaces there are prolongations of the 

 synovial cavity serving for their articulation with the carpus. 



At their_distal ends_the same four metacarpal bones are connected 



