Limbs: Upper Limb 117 



Bones. Time of Appearance of Centres. 

 Os magnum ... ist year. 



Unciform . . 2nd 



Cuneiform . . . 3 r d ,, 



Semilunar . . . 4th ,, 



! ca p hoki U-eth 



Trapezium . . . . j 



Trapezoid 7 tn 



Pisiform .... nth 



The metacarpals are ossified from two centres, one for the shaft and one for a 

 distal epiphysis, so that at birth the heads are cartilaginous, because the shaft centres 

 appear in the ninth week, whereas the epiphysial centres are found in the second year. 

 The thumb metacarpal is an exception, in that its epiphysis is at the proximal end, the 

 centre appearing in the third year : in about 6 per cent, of cases there is also a small 

 distal epiphysis, appearing later and uniting with the shaft in a few years. The normal 

 metacarpal epiphyses join the shafts between fifteen and twenty. Additional centres 

 are sometimes found for the styloid process of the middle metacarpal and for the 

 proximal end of the index metacarpal (3 per cent.). 



Phalanges. These are preformed in cartilage with the exception of the ungual 

 tubercle on the last phalanges : at one stage the cartilaginous terminal phalanges are 

 longer than the middle ones. Ossification starts in the shafts, except in the terminal 

 phalanges, where the primary centre is at the distal end, and at birth the proximal 

 ends of each phalanx are cartilaginous : here the epiphysial centres appear about the 

 second year. 



The shaft centres for the last phalanges come first, in the seventh to eighth week, 

 then those for the first phalanges, ninth week, and lastly, about the eleventh or twelfth 

 week, those for the middle row. The proximal epiphysial centres come first in the 

 first row, and later in the others. 



The last phalanx of the thumb is the earliest to present a centre in its shaft : this 

 is the first ossifying nucleus in the hand. 



Ossification of epiphyses appears to start about a year earlier in females in the 

 metacarpus and phalanges, and in them the fusion with the shaft is also earlier : in 

 male bones this occurs about eighteen to twenty. 



