148 



OSTEOLOGY. 



DEVELOPMENT OF THE HAND. 



The Carpal bones are each, developed by a single centre ; at birth they are all 

 cartilaginous. Ossification proceeds in the following order (fig. 96): in the os 

 magnum and unciform an ossific point appears during the first year, the former 

 preceding the latter ; in the cuneiform, at the third year ; in the trapezium and 

 semilunar, at the fifth year, the former preceding the latter ; in the scaphoid, at the 

 sixth year ; in the trapezoid, during the eighth year ; and in the pisiform, about 

 the twelfth year. 



Fig. 96. Plan of the Development of the Hand. 



Carpus 



1 centrefo reach bone 

 Alt cartilayinous at tirtfi 



Metacarpus 

 2 Centres far euch tone 

 If or Shaft 

 1for Digital Extremity 



except l-* 



PTial anyes 



2 Centres for each lo-ne 



I for Shaft 

 1forMetaca,rp-aI Extn. 



The Metacarpal bones are each developed by two centres : one for the shaft, and 

 one for the digital extremity, for the four inner metacarpal bones ; one for the 

 shaft and one for the base, for the metacarpal bone of the thumb, which, in this 

 respect, resembles the phalanges. Ossification commences in the centre of the 

 shaft about the sixth week, and gradually proceeds to either end of the bone ; 

 about the third year the digital extremities of the four inner metacarpal bones and 

 the base of the first metacarpal, commence to ossify, and they unite about the 

 twentieth year. 



The Phalanges are each developed by two centres : one for the shaft and one 

 for the base. Ossification commences in the shaft, in all three rows, at about the 

 sixth week, and gradually involves the whole of the bone excepting the upper 

 extremity. Ossification of the base commences in the first row between the third 

 and fourth years, and a year later in those of the second and third row. The two 

 centres become united, in each row, between the eighteenth and twentieth years. 



