HONES OF THE HAND. 



607 



not begin till between the twelfth ami fifteenth 

 years, and I'ruveillner states that of all the 

 bones of the skeleton it is tlie last in which the 

 process of ossification i- completed. 



II. Alitiifiir/'ii!, ((icrm. die Mittflhund ). 

 Five bonus constitute the metacarpus, the four 

 internal ones being parallel to each other, the 

 external one divernni 1 ^ 1 outwards at an acute 

 angle with the middle line of the hand. These 

 biines vary in length from about two inches and 

 a half to one inch six-eighths. They artirulale 

 inferior!) with the superior or metaearpal pha- 

 langes, and superiorly with the carpus. 



Each metaearpal bone presents two extremi- 

 ties, and a shaft or body between them. The 

 jiM/jiT<iir or ciirjial extremity is expanded and 

 "'due-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- 

 rarpal bone or to a carpal bone. The palmar 

 and dorsal surfaces are rough and irregular, 

 and arl'urd insertion to the ligaments which 

 streimthen the carpo-metacarpal joints. 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 ease of the mclatarsal bones, more 

 mi the side of flexion than on that of extension. 

 The shaft or tuxti/ is prismatic and slightly 

 curved, so as to present a concavity towards the 

 palmar surface, and a convexity to the dorsal. 



The metaearpal bones are numbered from 

 without inwards. The fint, 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 wkler 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 Hatter on its palmar and dorsal surfaces than 

 any of the others. 



The second metacaqxil bone is the lonyiM ; 

 it, however, exceeds the third by a very slight 

 difference. It is further distinguished from tin- 

 third by the diminutive size of the articular 

 facet on the radial side of its carpal extremity. 



The third niclacarpal bone, tiunii,'li shorter 

 than the second, is manifestly thicker and 

 stronger; this excess of developeincnt being 

 attributable to its aflbrdini; insertion to one of 

 the most powerful muscles of the hand, 

 namely, the adductor pollicis. 



The fourth and Jifiti metacarpal bones are 

 shorter and in every way smaller than the pre- 

 ceding ones. The fifth is shorter and somewhat 

 tlnekei than the fourth : it has no articular facet 

 on the ulnar side of its carpal extremity, but 

 pic -cuts a piomment tubercle in that situation 

 fed the inscitKm of the extensor carpi ulnan-. 



The ttriitture of the metacarpal bones is the 

 sum- as that of the long bones in general. 



Develtipemi-nt. There are two [mints of 

 ossification for each metaearpal bone, one for 

 the body and the carpal extremity, the other 

 for the digital extremity. The first metaearpal 

 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. Jn some 

 instances there arc three points of ossification 

 for each metacarpal bone. The bodies of the 

 metacarpal bones are completely ossified at 

 birth. Hetween 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 (digiti; Yr. Its doigtx ; derm. 

 die Finger). The ringers 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 iHitucarpal, the middle, and 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 

 riir,' finger, then the index, and last and least 

 the little finger. 



The Mictacar/ml phalanges have the following 

 general characters: 1st, a body slightly con- 

 cave from above downwards on the palmar 

 surface, and convex on the dorsal ; 3d, 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 isrough, non-articular, horseshoe-shai>ed, 

 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 ungiial 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 

 nones. There are two points of ossification, 

 one for the body and inferior extremity, the 

 other for the superior extremity. Tins last is 

 late in making its appearance, not until between 

 the third and seventh year, while the os^liea- 

 lion of the body commences at an early period 

 of mtra-utermc life. 



