OSSIFICATION OF THE BONES OF THE UPPER LIMB. 



109 



The metacarpal bones and phalanges are usually formed each from a principal centre for 

 the shaft and one epiphysis. The ossification of the shaft begins about the 8th or 9th 

 week. In the inner four metacarpal bones the epiphysis is at the distal extremity, while in 

 the metacarpal bone of the thumb and in the phalanges it is placed at the proximal extremity. 

 In many instances, however, there is also a distal epiphysis visible in the first metacarpal bone 

 at the age of 7 or 8 years, and there are even traces of a proximal epiphysis in the 

 second metacarpal. In the seal and some other animals there are always two epiphyses 

 in these bones. The epiphyses begin to be ossified from the 3rd to the 5th year, and are 

 united to their respective shafts about the 20th year. The terminal phalanges of the 

 digits present the remarkable peculiarity that the ossification of their shafts commences at the 

 distal extremity, instead of in the middle of their length, as is the case with the other 

 phalanges and with the long bones generally (Schafer and Dixey, Proc. Roy. Soc. xxx, 550. 

 and xxxi, 63). 



Fig. 121. OSSIFICATION OF THE BONES OF THE HAND. (R. Quain. ) 



A, the condition at birth. The carpus is entirely cartilaginous. Each of the metacarpal bones and 

 digital phalanges has its shaft ossified. 



B, at the end of the first year. The os magnum and unciform have begun to ossify. 



C, about the third year. Centres of ossification are seen in the pyramidal and in the proximal 

 epiphysis of the first and distal epiphyses of the other four metacarpal bones, and in the proximal 

 epiphyses of the first row of phalanges. 



D, at the fifth year. Centres have been formed in the trapezium and later in the lunar bone, 

 and in the epiphyses of the middle and distal phalanges : (the figure does not show them distinctly in 

 the middle phalanges). 



E, at about the ninth year. Centres have been formed in the scaphoid and trapezoid bones, and the 

 more developed epiphyses of the metacarpal bones and phalanges are shown in the first and second 

 digits separatsly. 



1, os magnum ; 2, unciform ; 3, pyramidal ; 4, lunar ; 5, trapezium ; 6, scaphoid ; 7, trapezoid ; 

 8, metacarpal bones, the principal pieces ; 8*, four metacarpal epiphyses ; 8', that of the thumb ; 9, 

 first phalanges ; 9*, their epiphyses ; 9', that of the thumb ; 10, second phalanges ; 10', epiphysis of 

 terminal phalanx of thumb ; 11, terminal phalanges of the fingers ; 11*, their epiphyses. 



