166 



THE SKELETON. 



digital extremity, and, running backward, converge to meet 4^gether a little 

 behind the centre of the bone and form a ridge which runs along^the rest of the 

 dorsal surface to the carpal extremity. This ridge separates two lateral, sloping 

 surfaces for the attachment of the Dorsal interossei muscles. 1 To the tubercles 

 on the digital extremities are attached the lateral ligaments of the metacarpo- 

 phalangeal joints. 



The carpal extremity, or base, is of a cuboidal form, and broader behind than 

 in front; it articulates above with the carpus, and on each side with the adjoining 

 metacarpal bones ; its dorsal and palmar surfaces are rough, for the attachment of 

 tendons and ligaments. 



The digital extremity, or head, presents an oblong surface, markedly convex 

 from before backward, less so from side to side, and flattened laterally ; it articu- 

 lates with the proximal phalanx ; it is broader and extends farther forward on the 

 palmar than on the dorsal aspect. It is longer in the antero-posterior than in the 

 transverse diameter. On either side of the head is a tubercle for the attachment 

 of the lateral ligament of the metacarpo-phalangeal joint. The posterior surface, 

 broad and flat, supports the Extensor tendons ; the anterior surface is grooved in 

 the middle line for the passage of the Flexor tendons, and marked on each side by 

 an articular eminence continuous with the terminal articular surface. 



Peculiar Characters of the Metacarpal Bones. 



The metacarpal bone of the thumb (Fig. 114) is shorter and wider than the 

 rest, diverges to a greater degree from the carpus, and its palmar surface is 



directed inward toward the palm. The shaft is 

 flattened and broad on its dorsal aspect, and does 

 not present the ridge which is found on the other 

 metacarpal bones ; it is concave from above down- 

 ward, on its palmar surface. The carpal extrem- 

 ity, or base, presents a concavo-convex surface, for 

 articulation with the trapezium ; it has no lateral 

 facets, but presents externally a tubercle for the 

 insertion of the Extensor ossis metacarpi pollicis. 

 The digital extremity is less convex than that of 

 the other metacarpal bones, broader from side to 

 side than from before backward. It presents on 

 its palmar aspect two distinct articular eminences 

 for the two sesamoid bones in the tendons of the 

 Flexor brevis pollicis, the outer one being the 

 larger of the two. 



The side to which this bone belongs may be 

 known by holding it in the position it occupies in the hand, with the carpal 

 extremity upward and the dorsal surface backward ; the tubercle for the 

 Extensor ossis metacarpi pollicis will point to the side to which it belongs. 



Attachment of Muscles. To four : the Flexor ossis metacarpi pollicis, the 

 Extensor ossis metacarpi pollicis, the Flexor brevis pollicis, and the First dorsal 

 interosseous. 



The metacarpal bone of the index finger (Fig. 115) is the longest and its base 

 the largest of the other four. Its carpal extremity is prolonged upward and 

 inward, forming a prominent ridge. The dorsal and palmar surfaces of this 

 extremity are rough, for the attachment of tendons and ligaments. It presents 

 four articular facets : three on the upper aspect of the base : the middle one of the 

 three is the largest, concave from side to side, convex from before backward, for 

 articulation with the trapezoid ; the external one is a small, flat, oval facet, for 

 articulation with the trapezium ; the internal one on the summit of the ridge is 



1 By these sloping surfaces the metacarpal bones of the hand may be at once differentiated from 

 the metatarsal bone of the foot. 



Tubercle 



For trapezium. For trapezium. 

 FIG. 114. The first metacarpal. (Left.) 



