2SO STUDIES IN THE EVOLUTION OF ANIMALS 



each of these bones in the human carpus, and in that of animals 

 which are in possession of the archetypal hand, leads to the belief 

 that the scaphoid is the result of fusion of the fourth and fifth bones 

 of the upper row, and the unciform the fusion of the first and 

 second bones of the inferior row.' This may be so, but let us 

 see what Sir W. H. Flower ^ has to say on the homologies of 

 carpal bones. 



'The determination of the homologies of the carpal bones of 

 the Cetacea with those of other mammalia is beset with diffi- 

 culties, and has consequently led to some differences of opinion 

 among those anatomists who have attempted it. Moreover, 

 every species appears liable to certain individual variations, and 

 sometimes the different sides of the same animal are not precisely 

 alike, either in arrangement or even the number of the carpal 

 ossifications. ... In many cases, as in the round-headed Dolphin, 

 the bones of the distal row of the carpus are reduced to two, which 

 appear to correspond best with the trapezoid and unciform, the 

 magnum being either absent or amalgamated with the trapezoid. 

 The trapezium appears never to be present (in the Cetacea) as a 

 distinct bone, although the first metacarpal so often assumes the 

 characters and position of a carpal bone that it may easily be 

 mistaken for it.' 



Further, some species of Woolly Spider Monkeys {Eriodes 

 arachnoides) have a rudiment of a thumb on one hand, and not a 

 trace of one on the other.^ 



Note that ' sometimes the different sides of the same animal are 

 not precisely alike, either in arrangement, or even the number of the 

 carpal ossifications! 



If the two sides of the same individual are liable to variation in 



^ Osteology of Mammals, p. 301, 3rd Edit. 

 ^ Royal Natural History, vol. i. p. 158. 



