THE MAMMALIA OF THE UIXTA FORMATION. 569 



converges to the centre of the carpns, without a defined median digital axis, and the 

 lunar spreads to the ectal or cntal side according as the respective growth of the 

 radius or ulna alters the major axis of the fore arm. 



5. In the Diplarthra the major axis of the fore arm passes through the radius, 

 and through the thiid digit (Mcsaxonia) or between the second and lliiiil digits 

 (P a r a X o n i a). The outwaid displacement of the entire ui)per upon the lower row 

 of carpals is apparent, not real ; the magnum and lunar are arrested in growth, and 

 the lunar remains almost directly in the mesaxial line ; what actually takes place is 

 the ental growth of the unciform and ectal growth of the scaphoid towards the 

 mesaxial line, thrusting the magnum and lunar apart. 



(i. This growth is affected by the i-eduction of the lateral digits in so far as this 

 alters their relation to the major axis of the metapodium. Where reduction leaves 

 the major axis between the third and fourth digits, this growth is arrested ; where it 

 leaves it directly through the third digit it is extreme ; where the third digit alone 

 transmits the main impact, the displacement is neutralized by the growth of the ele- 

 ments which directly support this digit (/. e., magnum and cuiK'ifoi'm 3). 



