THE DIGITAL PHALANGES. 



105 



The third bone articulates above with the os magnum, and on the sides with the 

 contiguous metacarpal bones ; at its posterior and outer angle it forms a projection 

 upwards, styloid process, immediately below which, on the dorsal aspect, is an im- 

 pression for the insertion of the extensor carpi radialis brevior. The fourth 

 articulates principally with the unciform bone above, but also by a small facet at 

 the posterior and outer corner with the os magnum : on its radial side are two 

 email rounded facets, and on the ulnar side a slightly concave semi-elliptical surface, 

 for articulation with the adjacent metacarpal bones. The fifth articulates above 

 with the unciform bone by means of a saddle-shaped surface directed slightly 

 outwards, and externally with the fourth metacarpal bone ; 

 while on its ulnar side there is a broad tuberosity for the 

 insertion of the extensor carpi ulnaris. 



THE DIGITAL PHALANGES 



The phalanges (mternodia) are fourteen in number, three 

 for each finger, but only two for the thumb. 



Those of the first roiv are slightly curved like the meta- 

 carpal bones. Their dorsal surfaces are smooth and transversely 

 convex ; the palmar are flat from side to side, and bounded by 

 rough margins, which give insertion to the fibrous sheaths of 

 the flexor tendons. Their proximal extremities are thick, and 

 articulate each by a transversely oval concave surface with 

 the corresponding metacarpal bone. Their distal extremities, 

 smaller and more compressed antcro-posteriorly, are divided by 

 a shallow groove into two condyles. 



Those of the middle row are four in number. Smaller 

 than those of the preceding set, they resemble them in form, 

 with this difference, that their proximal extremities present, on 

 the articular surface, a slight middle elevation and two lateral 

 depressions, adapted to articulate with the condyles of the first 

 phalanges. 



The terminal or ungual phalanges, five in number, have 

 proximal extremities similar to those of the middle row, but with 

 a depression in front, where the deep flexor tendon is inserted. 

 They taper towards their somewhat flattened and expanded free 

 extremities, which are rough and raised round the margins and 

 upon the palmar aspect in the so-called ungual process. 



Fig. 114. THE PHA- 

 LANGES OF THE MID- 

 DLE FINGEK: PALMAR 

 ASPECT. (G. D. T.) 



In each digit the proximal phalanx is the longest, and the distal 

 phalanx the shortest. Collectively, the phalanges of the middle finger 

 are the longest ; then follow in order, the ring, the index, and the 



little fingers, and lastly the thumb. The greater prominence of the index in relation to the 

 ring finger, which is observed sometimes in the complete hand, is due entirely to the length 

 of the metacarpal bone (Braune and Fischer, Arch. f. Anat., 1887). 



SESAMOID BONES. A pair of sesamoid bones is placed in the palmar wall of the 

 metacarpo-phalangeal articulation of the thumb ; and similar nodules, single or 

 double, are sometimes found in the corresponding joint of one or more of the other 

 fingers, most frequently of the index and little fingers. 



