THE METACARPUS. 



The metacarpal bone of the middle finger is a little smaller than the preceding : 

 it presents a pyramidal eminence (the styloid process) on the radial side of its 

 base (dorsal aspect) which extends upward behind the os magnum. The carpal, 

 articular facer 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 

 meracarpal bone, and on the ulnar side two small, oval facets, for articulation with 

 the fourth metacarpal. 



The side to which this bone belongs is easily recognized by the stvloid pro- 

 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. 



The metacarpal bone of the ring finger is shorter and smaller than the preced- 

 ing, and its base small and quadrilateral ; the carpal surface of the base present- 

 ing two facets, for articulation with the unciform and 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. 



The metacarpal bone of the little finger presents on its base one facet, which 

 is concavo-convex, and which articulates with the unciform bone, and one lateral, 

 articular facet, which articulates with the fourth metacarpal bone. On its ulnar 

 side is a prominent tubercle, for the insertion of the tendon of the Extensor carpi 

 ulnaris. The dorsal surface of the shaft is marked by an oblique ridge which 

 extends from near the ulnar side of the upper extremity to the radial side of 

 the lower. The outer division of this surface serves for the attachment of the 

 Fourth dorsal interosseous muscle ; the inner division is smooth and covered by 

 the Extensor tendons of the little finger. 



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

 upward, the side of the head which has a lateral facet will be that to which the 

 bone belongs. 



Articulations. Besides the phalangeal articulations, the first metacarpal bone 

 articulates with the trapezium ; the second with the trapezium, trapezoid, os 

 magnum, and third metacarpal bones; the third with the os magnum and second 

 and fourth metacarpal bones : the fourth with the os magnum, unciform. and 

 third and fifth metacarpal bones; and the fifth with the unciform and fourth 

 meracarpal. 



The 1ir*t has no lateral facets on its carpal extremity : the second has no 

 lateral facet on its radial side, but one on its ulnar side ; the third has one on 

 its radial and two on its ulnar side : the fourth has two on its radial and one on 

 its ulnar side : and the fifth has only one on its radial side. 



Attachment of Muscles. To the metacarpal bone of the thumb, four: the 

 Flexor r,sis metacarpi pollicis, Flexor brevis pollicis. Extensor ossis metacarpi 

 pollicis. and First dorsal interosseous. To the second metacarpal bone, six: 

 the Flexor carpi radialis. Extensor carpi radialis longior. Adductor obliquus 

 pollicis. First and Second dorsal interosseous. and First palmar interosseous. 

 To the third, six: the Extensor carpi radialis brevior. Flexor carpi radialis. 

 Adductor transversus pollicis. Adductor obliquus pollicis, and Second and Third 

 tl interosseous. To the fourth, three: the Third and Fourth dorsal and 

 iid palmar interosseous. To the fifth, five: the Extensor carpi ulnaris, 

 Flexor carpi ulnaris. Flexor ossis metacarpi minimi digiti, Fourth dorsal and 

 Third palmar interosseous. 



