1 8 A BOOK OF WHALES 



fully-developed fingers or toes, and often there are 

 less ; but rudiments of one or two additional digits 

 are believed to be represented by certain supple- 

 mentary bones at the side of the first and of the 

 last digit. 



In the ichthyopterygium, or fish fin, there is no 

 such clear distinction into the several regions which 

 characterise the cheiropterygium. The whole limb 

 is shorter, and often two or more pieces articulate 

 with the limb girdle. The distal cartilages are 

 generally more numerous than five ; but they are 

 not so much subdivided as they are in the cheirop- 

 terygium into a series of pieces following one another. 

 It is not possible in the ichthyopterygium to recog- 

 nise clearly the several regions of the cheiropterygium 

 arm, forearm, wrist, digits. 



Now there are two points in which the whale's 

 hand and arm have come to be slightly modified in 

 the direction of the Ichthyopterygium. In the first 

 place the distinction between hand and arm is com- 

 mencing to vanish. The proportions between the 

 bones is not so unequal as in typical mammals. The 

 radius and the ulna are short bones, and there is less 

 distinction between the bones of the carpus and 

 the ensuing metacarpus than is seen in terrestrial 

 mammals. This modification, however, has not gone 

 very far. As may be seen from the drawing on 

 p. 25, it is still perfectly easy to distinguish the 

 several elements of which the arm is made up. It 

 follows from this that the hand proper is larger in 

 comparison with the arm than it is in terrestrial 



