THE CARPUS 



221 



in the lower end; and at the fifth year, in the upper end. The upper epiphysis fuses with the 

 body at the age of seventeen or eighteen years, the lower about the age of twenty. An additional 

 center sometimes found in the radial tuberosity, appears about the fourteenth or fifteenth year. 



Appears 

 fifth year 



Unites with body 

 about puberty 



Appears at 

 second year 



Unites with body 

 about twentieth 

 year 



Lower extremity 



FIG. 217. Plan of ossification of the radius. 

 From three centers. 



Fio. 218. Epiphysial lines of radius in a young 

 adult. Anterior aspect. The line of attachment of the 

 articular capsule of the wrist-joint is in blue. 



THE HAND. 



The skeleton of the hand (Figs. 219, 220) is subdivided into three segments: the 

 carpus or wrist bones; the metacarpus or bones of the palm; and the phalanges or 

 bones of the digits. 



The Carpus (Ossa Carpi). 



The carpal bones, eight in number, are arranged in two rows. Those of the 

 proximal row, from the radial to the ulnar side, are named the navicular, lunate, 

 triangular, and pisiform ; those of the distal row, in the same order, are named the 

 greater multangular, lesser multangular, capitate, and hamate. 



Common Characteristics of the Carpal Bones. Each bone (excepting the pisi- 

 form) presents six surfaces. Of these the volar or anterior and the dorsal or posterior 

 surfaces are rough, for ligamentous attachment; the dorsal surfaces being the 

 broader, except in the navicular and lunate. The superior or proximal, and inferior 

 or distal surfaces are articular, the superior generally convex, the inferior concave; 

 the medial and lateral surfaces are also articular where they are in contact with 

 contiguous bones, otherwise they are rough and tuberculated. The structure in 

 all is similar, viz., cancellous tissue enclosed in a layer of compact bone. 



Bones of the Proximal Row (upper row). The Navicular Bone (os namculare manus; 

 scaphoid bone) (Fig. 221). The navicular bone is the largest bone of the proximal 

 row, and has received its name from its fancied resemblance to a boat. It is situated 

 at the radial side of the carpus, its long axis being from above downward, lateral ward, 

 and forward. The superior surface is convex, smooth, of triangular shape, and artic- 



