BONES OF THE HAND. 



507 



not begin till between the twelfth and fifteenth 

 years, and Cruveilhier states that of all the 

 bones of the skeleton it is the last in which the 

 process of ossification is completed. 



II. Metacarpus (Germ, die Mittelhand). 

 Five bones constitute the metacarpus, the four 

 internal ones being parallel to each other, the 

 external one diverging outwards at an acute 

 angle with the middle line of the hand. These 

 bones vary in length from about two inches and 

 a half to one inch six-eighths. They articulate 

 inferiorly with the superior or metacarpal pha- 

 langes, and superiorly with the carpus. 



Each metacarpal bone presents two extremi- 

 ties, and a shaft or body between them. The 

 superior or carpal extremity is expanded and 

 wedge-shaped, the broader part being towards 

 the dorsal aspect. Three articular surfaces 

 exist on each ; one, the most extensive, on the 

 superior or carpal surface, for articulation with 

 a carpal bone ; the other two on the radial and 

 ulnar surfaces, adapted to the adjacent meta- 

 carpal bone or to a carpal bone. The palmar 

 and dorsal surfaces are rough and irregular, 

 and afford insertion to the ligaments \vhich 

 strengthen the carpo-metacarpal jointsv^The 

 interior or digital extremity is in the form of a 

 rounded head, flattened on each side, where 

 we notice a depression, and behind it a tubercle 

 which affords insertion to the lateral ligament 

 of the joint. The smooth articular surface of 

 the head extends further upon the palmar sur- 

 face of the bone than upon its dorsal surface, 

 or, as in the case of the metatarsal bones, more 

 on the side of flexion than on that of extension. 

 The shaft or body is prismatic and slightly 

 curved, so as to present a concavity towards the 

 palmar surface, and a convexity to the dorsal. 



The metacarpal bones are numbered from 

 without inwards. The first, or that of the 

 thumb, is the shortest of all and likewise the 

 thickest. Its carpal extremity will likewise 

 serve to distinguish this bone; it wants the 

 cuneiform shape, and is rather wider on its 

 palmar than its dorsal surface. It has no arti- 

 cular facets on its sides, being articulated with 

 the trapezium alone by means of a surface 

 which is concave from before backwards, and 

 Convex from side to side ; the body of this bone 

 is flatter on its palmar and dorsal surfaces than 

 any of the others. 



The second metacarpal bone is the longest ; 

 it, however, exceeds the third by a very slight 

 difference. It is further distinguished from the 

 third by the diminutive size of the articular 

 facet on the radial side of its carpal extremity. 



The third metacarpal bone, though shorter 

 than the second, is manifestly thicker and 

 stronger; this excess of developement being 

 attributable to its affording insertion to one of 

 the most powerful muscles of the hand, 

 namely, the adductor pollicis. 



The fourth and fifth metacarpal bones are 

 shorter and in every way smaller than the pre- 

 ceding ones. The fifth is shorter and somewhat 

 thicker than the fourth : it has no articular facet 

 on the ulnar side of its carpal extremity, but 

 presents a prominent tubercle in that situation 

 for the insertion of the extensor carpi ulnaris. 



The structure of the metacarpal bones is the 

 same as that of the long bones in general. 



Developement. There are two points of 

 ossification for each metacarpal bone, one for 

 the body and the carpal extremity, the other 

 for the digital extremity. The first metacarpal 

 bone, however, according to Cruveilhier, offers 

 an exception to this, inasmuch as its carpal 

 extremity is developed from a point of ossifica- 

 tion distinct from that of the body. In some 

 instances there are three points of ossification 

 for each metacarpal bone. The bodies of the 

 metacarpal bones are completely ossified at 

 birth. Between the second and third years 

 appear the points for the inferior extremity in 

 the four inner bones and the superior extremity 

 in the first, but the complete fusion of the 

 extremities with the shafts does not take place 

 till near the twentieth year. 



III. Fingers ( digit i; Fr. les doits ; Germ. 

 die Finger). The fingers differ strikingly from 

 the toes as regards their length, to which, in- 

 deed, is due their greater mobility. They are 

 numbered in proceeding from the radial to the 

 ulnar side of the hand. All except the thumb 

 are composed of three phalanges, the superior 

 or metacarpal, the middle, ana 1 the inferior or 

 lingual: in the thumb the middle phalanx is 

 absent. The fingers differ considerably in length ; 

 the thumb is by far the shortest, and the middle 

 finger is the longest. Next in length is the 

 ring finger, then the index, and last and least 

 the little finger. 



The metacarpal phalanges have the following 

 general characters : 1st, a body slightly con- 

 cave from above downwards on the palmar 

 surface, and convex on the dorsal ; 2d, a supe- 

 rior or metacarpal extremity more expanded 

 than the inferior, hollowed into an articular 

 surface for the head of the metacarpal bone ; 

 and 3d, an inferior extremity, having a pulley- 

 like surface for articulation with the middle 

 phalanx. The metacarpal phalanges are the 

 longest. 



The middle phalanges present the same cha- 

 racters as the preceding as regards the body. 

 The superior extremity has a pulley-like articu- 

 lar surface, convex transversely; that of the 

 inferior extremity being concave in the same 

 direction. 



The ungual phalanges are readily distin- 

 guished by the inferior or ungual extremity, 

 which is rough, non-articular, horseshoe-shaped, 

 with the convexity directed downwards. It is 

 this part of the bone which supports the nail. 

 The superior extremity is articulated with the 

 middle phalanx by a pulley-like surface, con- 

 cave transversely. The ungual phalanx of the 

 thumb is considerably larger than that of any 

 of the other fingers. 



In point of structure and developement the 

 phalanges scarcely differ from the metacarpal 

 bones. There are two points of ossification, 

 one for the body and inferior extremity, the 

 other for the superior extremity. This last is 

 late in making its appearance, not until between 

 the third and seventh year, while the ossifica- 

 tion of the body commences at an early period 

 of intra-uterine life. 



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