THOEACIC LIMBS 



633 



The Shaft and Head present no peculiarities. 



Determination. When the bone is held with the dorsal surface 

 upward and the proximal surface toward the student, the shelf-like 

 radial part of the proximal surface of the base will serve to distinguish 

 the bone from the other metacarpals, and the straight ulnar border is 

 on the side to which the bone belongs. 



FIG. 501. 

 Proximal End. 



With Unciform.- 



With Third 



Metacarpal. 



Palmar Side. 



Dorsal Side. 



FOURTH LEFT METACARPAL, RADIAL SURFACE OF BASE AND 



PART OF SHAFT. 



Articulation. The fourth metacarpal articulates above with the 

 magnum and uuciform, on the radial side with the third metacarpal, on 

 the ulnar side with the fifth metacarpal, and below with the proximal 

 phalanx of its own digit. 



Muscular Attachments. The palmar aspect of the shaft gives 

 origin near the base to the third palmar interosseous, and along the 

 ulnar side to the fourth dorsal interosseous. A strong ligament from 



FIG. 502. 



Proximal End. 



T( ith Fifth Metacarpal. 



Ulnar Side. 



With Unciform. 



| With Third Metacarpal. 



Radial Side. 



FOURTH LEFT METACARPAL, PALMAR SURFACE OF BASE AND 



PART OF SHAFT. 



the radial tip of the head of the pisiform is inserted into the proximal 

 end of the shaft at the ulnar side of the palmar aspect, and may be 

 regarded as the continuation of the tendon of the flexor carpi ulnaris 

 muscle. 



Ossification. The fourth metacarpal is developed from two 

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



