THE CONNECTIVE TISSUES AND THE SKELETAL SYSTEM. 



169 



(ulnar, pyramidal, cuneiform) . The distal row is composed of four elements 

 which are the forerunners of the large multangular (trapezium), small multangu- 

 lar (trapezoid), capitate (os magnum), and hamatate or hooked (unciform). In 

 addition to the cartilages mentioned, several others also appear in an inconstant 

 way in different individuals. Two of these are important. One appears on 

 the ulnar side of the proximal row and is the forerunner of the pisiform; the 

 other is situated between the two rows and may either disappear entirely or fuse 

 with the navicular. Ossification does not begin in the carpal cartilages until 

 after birth; it begins in the hamatate and capitate during the third year, in the 



Metacarpals 



Large 

 multangular 



Capitate 

 Navicular 



Radius 



FIG. 145. Skiagram of right hand of 5 year old girl. (Courtesy of Dr. Edward Learning). 

 The ossification centers are indicated by the darker areas. 



others at later periods, and is completed only when the growth of the individ- 

 ual ceases. The fact that the hamatate ossifies from two centers indicates 

 that it is probably derived phylogenetically from two bones. Comparative 

 anatomy teaches that the accessory cartilages in the human wrist are repre- 

 sentatives of structures which are normally present in the lower forms. 



The metacarpals and phalanges are preformed in cartilages which correspond 

 in shape to the adult bones. A center of ossification appears in each cartilage 

 and produces the shaft of the bone. Only one epiphysis develops on each 

 metacarpal and phalanx. In each metacarpal it develops at the distal end, 



