THE CARPUS. 



309 



THE HAND. 



The hand is composed of the carpus or wrist, consisting of eight small bones 

 arranged in two rows, which is succeeded by five rays of four segments each, — 

 namely, a metacarpal bone and three phalanges, excepting the thumb, in which one 

 phalanx is wanting. 



THE CARPUS. 



There are eight carpal bones arranged in two rows of four each. The first row 

 includes, named from the radial towards the ulnar side, the scaphoid, the seniihmar, 

 the cuneiform, and the pisiform ; the second row, the trapezium, the trapezoid, the 

 OS magnum, and the unciform. Exceptionally, several other bones may occur, due 

 to the persistence of centres laid down in early foetal life, which normally fuse with 

 other centres or disappear. Thus there is much in favor of the view that the plan 

 of the carpus is more complicated. This point is further considered in the dis- 

 cussion of variations (page 313). The pisiform of the first row, whatever may be 

 its morphological significance, is in man practically nothing but a sesamoid bone 

 in the tendon of the flexor carpi ulnaris, resting on the palmar surface of the cunei- 

 form, and having no share in the mechanics of the wrist excepting as giving attach- 

 ment to a part of the anterior annular ligament. The first row, therefore, consists 

 really of the three first-mentioned bones, which are joined into one flexible piece by 

 interosseous ligaments. The upper end of this combination bears an egg-shaped 

 articular surface for the wrist-joint, to which all three bones contribute. Its lower 

 side has a concavo-convex oudine, the concavity receiving the inner two bones and 

 the convexity bearing the outer two of the second row. The latter consists of four 

 bones connected by ligaments : the trapezium, for the thumb ; the trapezoid and 

 OS magnum, for the next two fingers ; and the unciform, for the ring and litde 

 fingers. The dorsal side of the carpus is slighdy convex and the palmar deeply 

 concave, forming bv its middle the floor of a deep canal, bridged by the anterior 

 annular ligament, which runs between bony elevations on each side of the carpus. 

 To shorten the description, it may be said that little depressions for ligaments can 

 be seen on well-marked bones near their edges on the dorsal and palmar aspects, 

 especially the former. 



The scaphoid [os naviculare], or boat-shaped bone, is the largest and most 

 external of the first row. It is a flattened elongated disk placed with the long axis 

 running outward and downward. It receives its name from being convex on the 

 upper and outer side for the radius and concave on the opposite side for the head 

 the OS magnum. Nearly corresponding with the long axis is the long and very 



Fig. 321. 



For trapezium 



Fig. 322. 



Tuberosity 



External 

 surface 



For trapezoid 



For radius 

 Right scaphoid, dorsal aspect. 



Dorsal 

 surface 



For 

 magnum 



For. 

 semilunar 



Tuberosity 



Palmar surface 

 Right scaphoid, inner aspect. 



narrow dorsal surface. The palmar surface is broader, runs more downward, and 

 the outer end rises into the tuberosity of the scaphoid, from which part of the anterior 

 annular ligament springs. The convex proximal surface for the radius is wholly 

 articular ; the inner edge is straight, the dorsal and palmar converge externally ; .it 

 tends to encroach on the dorsal surface. Ititernally there are two surfaces, both 



