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THE METACARPUS. 2038 
in the second month after birth. According to Debierre (Jour. de VAnat. et de la Physiol. 
vol. xxii., 1886, p. 285), ossification takes place approximately as follows :— 
Os magnum ; : : . 11 to 12 months. 
Uneiform . : ; i . 12 to 14 months. 
Cuneiform . ; ; : » 3 years! 
Semilunar . : : 3 . 5 to 6 years. 
Trapezium . : , { . 6 years. 
Scaphoid —. . . 6 years. 
Trapezoid . : , 2 . 6 to 7 years. 
Pisttorm |. ; : : . 10 to 12 years. 
The same observer failed to note the appearance of a separate centre for the apophysis 
of the unciform, and records the occurrence of two centres for the pisiform. 
THE METACARPUS. 
The metacarpal bones form the skeleton of the palm, articulating proximally 
with the carpus, whilst by their distal extremities or heads they support the bones 
of the fingers. Five in number, one for each digit, they lie side by side and 
slightly divergent from each other, being separated by intervals, termed interosseous 
spaces. Distinguished numerically from without inwards, they all display certain 
common characters ; each possesses a body or shaft, a base or carpal extremity, and 
a head or phalangeal end. 
The shafts, which are slightly curved towards the palmar aspect, are narrowest 
towards their middle. Their dorsal surface is marked by two divergent lines 
which pass forward from the back of the base to tubercles on either side of the 
head. The: surface included between the two lines is smooth and of elongated 
triangular form. On either side of these lines two broad shallow grooves ‘wind 
spirally forward on to the palmar surface, where they are separated in front by a 
sharp ridge which is continuous with a somewhat triangular surface which corre- 
sponds to the palmar aspect of the base. The grooved surfaces on either side of the 
shaft furnish origins for the interossei muscles. Close to the palmar crest is the 
opening of the nutrient canal, which is directed towards the 
carpal extremity, except in the case of the first metacarpal 
bone. 
The head (capitulum) is provided with a surface for 
articulation with the proximal phalanx. This area curves 
farther over its palmar than its dorsal aspect. Convex from 
before backwards and from side to side, it is wider anteriorly 
than posteriorly; notched on its palmar aspect, its edges form 
two prominent tubercles, which are sometimes grooved for 
the small sesamoid bones which may occasionally be found on 
the anterior surface of the joint. On either side of the head 
of the bone there is a deep pit, behind which is a pro- 
minent tubercle; to these are attached the lateral ligaments 
of the metacarpo-phalangeal joints. 
The bases (basis), all more or less wedge-shaped in form, 
articulate with the carpus; they differ in size and shape 
according to their articulation. 
Of the five metacarpal bones, the first, viz. that of the 
thumb, is the shortest and stoutest, the second is the longest, 
whilst the third, fourth, and fifth display a gradual reduction 
in length. 
The four inner bones articulate by their bases with each 
other, and are united at their distal extremities by ligaments. 
They are so arranged as to conform to the hollow of the paln, 
being concave from side to side anteriorly, and convex posteriorly. The first meta- 
carpal differs from the others in being free at its distal extremity, whilst its 
proximal end possesses only a carpal articular facet. 
The first metacarpal bone is the shortest and stoutest of the series. Its shaft 
Shaft 
Trapezium 
Fic. 149.—First RIGHT 
METACARPAL BONE. 
