ii2 Anatomy of Skeleton 



the outer side and altogether on the ulnar side, by rough areas for interosseous liga- 

 ments. 



The styloid process may be short, separating the index metacarpal from the os 

 magnum, or may be larger and longer, extending between these to reach the trapezoid. 

 It may be a separate free ossicle, or this may have fused secondarily, not with the meta- 

 carpal, but with the os magnum or, more rarely, with the trapezoid. 



Fourth, or Ring-Finger, Metacarpal. This can be recognised because it mani- 

 festly has not the character of the bones already considered, yet has metacarpal facets 

 on each side, and not on one side only, as is the case in the fifth .metacarpal in fact 

 it can be recognised mainly by its negative characters. The ulnar metacarpal facet 

 is single, the radial double. The carpal facet, for unciform, is continuous with the 

 single inner facet, but only indirectly with the posterior of the two outer ones, through 

 the medium of an obliquely-cut surface for the os magnum. It is cut off from the 

 anterior one by an area for the strong interosseous ligament connecting os magnum, 

 unciform, and the fourth metacarpal, and this ligament may be enlarged at the expense 

 of the anterior facet. 



Fifth, or Little-Finger, Metacarpal. Distinguished by its possession of a meta- 

 carpal facet on one side only : the non-articular inner side presents a prominent tubercle 

 near the dorsum for the insertion of the ulnar extensor. The carpal and metacarpal 

 facets are continuous round the outer margin cf the base. 



The shafts of the bones can also be distinguished from each other. That of the 

 first metacarpal has been considered already, and the markings on the others can be 

 examined now. 



The shafts are moulded by the interosseous muscles that are so closely applied 

 to them. A glance at the dorsal aspect of the metacarpus shows that the greater 

 breadth of the distal part of this surface in each bone is due to the encroachment of 

 the dorsal interossei on the proximal portion, and it is interesting to observe that the 

 extension of these muscles dorsally is most marked when there is a corresponding palmar 

 interosseous on that side of the bone : thus the proximal part of the dorsal surface or 

 ridge is pushed towards the outer side on the index metacarpal and to the inner side 

 in the fourth and fifth bones, an obliquity that is very marked in some specimens. 



Examine the sides of the shafts. The interossei have short tendinous fibres mixed 

 with their fibres of origin, and therefore there is a very slight roughness visible over 

 their areas ; but the finger and eye will have no difficulty in finding the fine cleanly- 

 cut line that marks the separation between dorsal and palmar interosseous, and in well- 

 marked bones the areas can be almost completely mapped out in this way. Fig. 92 

 shows these origins : the upper row is a view of the radial aspect of the bones ; in the 

 lower row they are seen from the inner side. 



It is evident that no two of these bones are alike in their markings for interossei, and it is 

 possible to put the bones in their right order from their shafts alone, provided that the sides to which 

 they belong are known. Observe also that the nutrient foramina are on the radial side in the three 

 inner bones, and on the ulnar side in the outer two : the canal descends in the first but ascends in 

 the other metacarpals, so being in accord with the rule that the canal is directed away from the 

 " growing end " of the bone, for there is normally only one epiphysis on these bones, and it forms 

 the base of the first metacarpal but the distal ends of the others. 



The inner side ot the fifth shaft receives the insertion of the Opponens of the little 

 finger : this belongs morphologically to the group of palmar interossei, being the ulnar 

 belly of the metacarpal flexor of the finger, which has extended its insertion proxi- 



