THE BONES OF THE UPPER LIMB 2ii 



adductor transversus pollicis, and the shaft also affords origin to 

 the second and third dorsal interossei. 



Articulations. — Superiorly with the os magnum, and the second 

 and fourth metacarpal bones, and inferiorly with the first phalanx 

 of the middle finger. 



The Fourth Metacarpal Bone. — This is shorter than the third, and 

 its base is small. The outer side of the base presents two circular 

 facets, separated by a rough vertical groove, for the third metacarpal. 

 The inner side has a semi-oval facet for the fifth metacarpal. The 

 superior surface presents two facets. One is large for the unci- 



Intemal Surface. 



For 4th Metacarpal^rt:;^^:; 



For Os Magnum 



— External Surface 

 Medullary Foramen 



•For 2nd Metacarpal 



Styloid Process 



Fig. 123. — The Third Right Metacarpal Bone. 

 A, Internal View; B, External View. 



form, whilst the other, situated at the outer and posterior part, 

 is small for the os magnum. The shaft gives origin to the third 

 and fourth dorsal, and second palmar, interossei. 



Articulations. — Superiorly with the os magnum, unciform, and 

 third and fifth metacarpals, and inferiorly with the first phalanx 

 of the ring finger. 



The Fifth Metacarpal Bone.— This is shorter than the fourth, but 

 longer than the first. The superior surface of the base presents a 

 quadrilateral facet for the tmciform. The outer side has a semi-oval 

 facet for the fourth metacarpal, and the inner side presents a rounded 

 tubercle for the insertion of the extensor carpi ulnaris. The inner 



