THORACIC LIMBS 627 



radial side of the proximal surface of the base of the third metacarpal, 

 and articulates for nearly its whole length with two facets on the radial 

 side of the magnum. The concave surface below this margin receives 

 a projection from the contiguous side of the base of the third meta- 

 carpal. Below this concavity, and down to the oblique groove for the 

 radial artery, the surface is rough for the attachment of the inter- 

 osseous ligament. 



The Shaft does not present any striking peculiarity. Its radial 

 border is concave. On its dorsal surface, which faces slightly to 

 the radial side, just below the oblique groove, is a swelling where 

 the tendon of the extensor carpi radialis longior is inserted. The 

 proximal part of the palmar surface gives attachment to the first 

 palmar interosseous and the adductor pollicis, and along the radial 

 side of the same surface arise the first dorsal interosseous and ad- 

 ductor pollicis muscles. On the palmar side of the ulnar border a 

 short distance below the base is the point of insertion of the flexor 

 carpi radialis muscle. 



The Head differs from the heads of the third and fourth meta- 

 carpals in being somewhat flattened on the ulnar side and presenting 

 on the radial side a prominence which is continuous with the tubercle 

 at the end of the lateral border of the shaft by passing behind the 

 lower end of the transverse groove which separates the head from the 

 shaft. 



Determination. The second metacarpal may be distinguished 

 from the others by the oblique position of the base. When the 

 bone is held with the dorsal surface upward and the proximal sur- 

 face toward the student, the base points to the side to which the bone 

 belongs. 



Articulation. The second metacarpal articulates on the radial 

 side with the first metacarpal and with the trapezium ; above, with 

 the trapezoid ; on the ulnar side, with the magnum and the third 

 metacarpal ; and below, with the proximal phalanx of the digit. 



Muscular Attachments. The second metacarpal offers attach- 

 ment by the dorsal surface to the extensor carpi radialis longior ; 

 by the palmar surface to the first dorsal interosseous, the first palmar 

 interosseous, the adductor pollicis, and the flexor carpi radialis. 



Ossification. The second metacarpal is developed from two 

 centres, one for the shaft and one for the head. 



