2IO A MANUAL OF ANATOMY 



pollicis. The dorsal aspect at its outer part gives insertion to the 

 extensor carpi radiahs longior, and at its inner part to a small slip 

 of the extensor carpi radialis brevior, there being a notch between 

 the two impressions. The shaft gives origin to the first and second 

 dorsal, and first palmar, interossei. 



Articulations. — Superiorly with the trapezium, trapezoid, and os 

 magnum, internally with the third metacarpal, and inferiorly with 

 the first phalanx of the index finger. 



Head 



Palmar Depression ^ 

 Dorsal Tubercle ^ " 



Medullary Foramen 

 Internal Surface.- 



External Surface 



For Trapezium 



For 3rd Metacarpal For Os Magnum 



For Trapezoid 



Fig. 122. — The Second Right Metacarpai. Bone. 

 A, Internal View; B, External View. 



The Third Metacarpal Bone.— This is next in length to the second. 

 Its distinctive character is the styloid process at the base. The 

 superior surface of the base articulates with the os magnum. The 

 outer side presents an antero-posterior facet, notched at its lower 

 border, for the second metacarpal. The inner side presents two 

 circular facets, separated by a rough vertical groove, for the fourth 

 metacarpal. The palmar aspect gives insertion to a slip of the flexor 

 carpi radialis, and origin to a portion of the adductor obliquus 

 pollicis. The dorsal aspect externally gives insertion to the prin- 

 cipal part of the extensor carpi radialis brevior, and it is projected 

 upwards at its outer angle into the styloid process. The anterior 

 border of the shaft, over its distal two- thirds, gives origin to the 



