THE PHALANGES 



137 



Ossification. — Each metacarpal is ossified from two centres. Tiie nucleus for 

 the shaft appears al)out the eighth week of embryonic life. At l)irth the shafts are 

 well ossified, but each end is capped by a piece of cartilage. In the case of the 

 first metacarpal, a centre for the epiphysis appears at the proximal end in the 

 course of the third year. The bases of the remaining metacarpals are ossified from 

 the shaft, but an epiphysis forms for the head of each bone in the third year. The 

 bones are usually consolidated by the twentieth year. 



In many cases the first metacarpal has two epiphyses, one at the base and an 

 additional one at the head; the latter is never so large as in the other metacarpal 

 bones. 



The third metacarpal occasionally has an additional nucleus for the prominent' 

 styloid i^rocess which constitutes such a distinguishing feature of this bone. 



The styloid process sometimes remains distinct, and is then known as the 

 styloid bone. Occasionally it fuses with the trapezoid or magnum. 



THE PHALANGES 



The phalanges are the bones of the fingers. They number in all fourteen: the 

 thumb has two, the other fingers three each. 



Each phalanx has a shaft, which is broad and slightly concave on the palmar. 



Fig. 149. — The Phalanges of the Third Digit of the Hand. (Dorsal view.) 



THIRD TERMINAL OR UNGUAL 

 PHALANX 



SECOND PHALANX 



FIRST PHALANX 



rounded and smooth on the dorsal aspect. The sides of the palmar surface are 

 raised where they give attachment to the sheaths of the flexor tendons. The base 

 of each phalanx of the first row presents a glenoid fossa which })lays upon the 

 convex head of the metacarpal Ijoiie. The distal end is surmounted by miniature 

 condyles. 



