Limbs : Upper Limb 



105 



the various bones have, in general, larger dorsal than palmar surfaces, a feature well 

 exemplified in the trapezoid. 



The flexor tendons, lying in the concavity of the carpus, are covered by the anterior 

 annular ligament, which is a purely carpal structure and is attached to the prominent 

 margins of the concavity that is, it is fastened externally to the trapezium and 

 tuberosity of scaphoid, and internally to the pisiform, hook 

 of unciform, and piso-uncinate ligament which connects these 

 two. When the anterior annular ligament is in position the 

 tunnel under it is floored by the whole front surfaces of os 

 magnum, trapezoid, and semilunar, by a large part of sca- 

 phoid, and by very small margins of trapezium, unciform 

 and cuneiform : all these bony surfaces are of course covered 

 by ligaments. The remainder of the trapezium and scaphoid 

 project beyond the line of outer attachment of the ligament, 

 and the remainder of unciform and cuneiform project beyond 

 its inner attachment, and the projecting areas thus provided, 

 covered by ligamentous tissue, are utilised for the origin of 

 muscles of the thenar and hypothenar eminences respectively. 

 The figure (Fig. 84) shows this, and likewise indicates how 

 these muscles also arise from the annular ligament. The 

 ligament is really the thickened front wall of the " flexor 

 sheath," and the general structure of the palm can be under- 

 stood from the figure, for it shows three compartments, a 

 central one that is the flexor sheath, and two side ones that 

 contain the thenar and hypothenar muscles. 



On its dorsal surface the carpus is covered largely by 

 ligaments and crossed by the posterior carpal arch and other 

 arteries under cover of the extensor tendons running to the 

 digits and metacarpus. These tendons are covered as they 

 lie on the radius by the posterior annular ligament this is 

 directed downwards and inwards, having no attachment to 

 the ulna, but reaching the inner part of the carpus, to which 

 it is attached, sonie of the fibres turning round this inner 

 border to reach the pisiform and anterior annular ligament. 

 This arrangement is in accordance with the fact that the 

 carpus moves with the radius in supination and pronation, 

 and any attachment to the ulna except in the axis of rota- 

 tion would interfere with such movement. 



THE METACARPUS. Each of the five metacarpal bones 

 has a shaft, a proximal base, and a distal head. With the 

 exception of that of the thumb, each base presents side articu- 

 lations for its neighbouring metacarpals in addition to the 

 basal carpal facet or facets. 



Each shaft is thick and strong, and, except in the thumb, widens on its dorsal 

 aspect as it is followed to the strong, square-cut head ; this appearance of the shaft 

 and head is one of the characters in which these bones differ from the corresponding 

 metatarsals in the foot (Fig. 85). The five bones make a radiating series with inter- 

 vening spaces that are filled by the Interossei muscles which arise from the shafts of 

 the bones. 



PHALAXGES. -All the first phalanges have oval concave facets at their proximal 



FIG. 85. To illustrate the 

 contrast between meta- 

 carpals and metatarsals, 

 and between phalanges 

 of hand and foot ; 

 slightly exaggerated. 

 Notice the strong shaft 

 of the metacarpal widen- 

 ing toward the head, 

 which is heavy and 

 square-cut, and compare 

 this with the narrow, 

 compressed shaft and 

 head of the metatarsal, 

 with its heavy base. The 

 hand phalanx is broad, 

 strong and flattened in 

 the shaft, whereas that 

 of the foot has a rounded 

 feeble shaft with heavy 

 ends. 



