THE METACARPUS 



203 



The metacarpal bone of the middle finger (os metacarpale III) (Fig. 163) is a 

 little smaller than the preceding; it presents a pyramidal eminence, the styloid 

 process (processus styloideus), on the radial side of its base (dorsal aspect), which 

 extends upward behind the os magnum; immediately below this, on the dorsal 

 aspect, is a rough surface for the attachment of the Extensor carpi radialis brevior. 

 The carpal, articular facet is concave behind, flat in front, and articulates with the 

 os magnum. On the radial side is a smooth, concave facet, for articulation with 

 the second metacarpal bone, and on the ulnar side two small, oval facets, for articu- 

 lation with the fourth metacarpal. 



The side to which this bone belongs is easily recognized by the styloid process on the radial 

 side of its base. With the palmar surface uppermost and the base toward the student, this process 

 points toward the side to which the bone belongs. 



Attachment of Muscles. To six Extensor carpi radialis brevior, Flexor carpi radialis, 

 Adductor transversus pollicis, Adductor obliquus pollicis, and Second and Third dorsal inter- 



, ... trapezium. 

 For trapezoid. ^.,. _ 



FIG. 162. The second metacarpal. (Left.) 



V 



, For third metacarpal 

 for os magnum. 



6ty> 



process, metacarpal. 



For os magnum. 



FIG. 163. The third metacarpal. (Left.) 



The metacarpal bone of the ring finger (05 metacarpale IV) (Fig. 164) is shorter 

 and smaller than the preceding, and its base small and quadrilateral; the carpal 

 surface of the base presenting two facets, a large one internally, for articulation 

 with the unciform, and a small one externally, for the os magnum. On the 

 radial side are two oval facets, for articulation with the third metacarpal bone; 

 and on the ulnar side a single concave facet, for the fifth metacarpal. 



If this bone is placed with the base toward the student and the palmar surface upward, the 

 radial side of the base, which has two facets for articulation with the third metacarpal bone, will 

 be on the side to which it belongs. If, as sometimes happens in badly marked bones, one of these 

 facets is indistinguishable, the side may be known by selecting the surface on which the larger 

 articular facet is present. This facet is for the fifth metacarpal bone, and would therefore be 

 situated on the ulnar side that is, the one to which the bone does not belong. 



Attachment of Muscles. To three the Third and Fourth dorsal and Second palmar inter- 



The metacarpal bone of the little finger (os metacarpale V) (Fig. 165) presents 

 on its base one facet, which is concavo-convex, and which articulates with the 



