G34 MAMMALIAN ANATOMY 



THE FIFTH METACARPAL BONE. 



General Description. The fifth metacarpal is one-third shorter 

 than the third, and about one-sixth shorter than the second. Its 

 peculiarities lie in the shape of the base, in the shaft, and in the head. 



The Base differs from that of all the others in having no articular 

 surface on the ulnar side, as it is the last bone on that side of the hand. 



The proximal surface is three times as long as it is wide, strongly 

 convex from before backward, and flat from side to side. Its radial 

 border is sharp and straight; the ulnar border is curved, and meets the 

 radial border in front and behind at angles, of which the palmar is 

 the more obtuse. It faces directly upward, but its long axis is directed 

 backward and to the radial side. Its ulnar border passes without a 

 sharp break into the roughened tuberosity of the ulnar surface of the 

 base. Almost the entire proximal surface is occupied by a facet, which 

 articulates with the ulnar side of the distal surface of the unciform. 



The radial surface of the base (Fig. 503) lies in a plane at right 

 angles to the plane of the proximal surface. Its upper border is 



FIG. 503. 

 Proximal End. 



With Fourth Metacarpal.- 



Palmar Side. l\ Dorsal Side. 



FIFTH LEFT METACARPAL, RADIAL SURFACE OF BASE AND 



PART OF SHAFT. 



strongly arcuate, following the dorso-palmar curve of the proximal 

 surface and passing into the dorsal side of the radial border of the 

 shaft. The palmar side forms a prominent hook, under which it is 

 continuous with the palmar border of the shaft. 



The upper part of the surface is flat, and is a crescentic articular 

 facet for the contiguous side of the fourth metacarpal. This facet is 

 wider behind than in front, where it passes to the dorsal side of a 

 sharp ridge, which runs from the surface in an oblique direction 

 downward and forward and fits into the depression on the ulnar side 

 of the base of the fourth metacarpal. Below and behind the ridge 

 the surface is convex for the attachment of ligaments. 



