MANUAL OF ZOOLOGY. 



gather in the adult, and form a single mass which is known 

 as the " canon-bone " (fig. 184, ca). In the Horse, in which the 

 foot consists of no more than a single digit, there is only a 

 single metacarpal bone, on each side of which are two little bony 



spines the so-called " splint- 

 bones " which are attached 

 superiorly to the carpus. These 

 are to be regarded as rudimen- 

 tary metacarpals ; but by Cuvier 

 they were looked upon as im- 

 perfect fingers. In most of the 

 other Ungulates there are at 

 least three metacarpals, and in 

 the Elephants there are five. 



The normal number of digits 

 is five, but they vary from one 

 to five. The middle finger is 

 the longest and most persistent 

 of the digits of the fore-limb; 

 and in the Horse it is the only 

 one which is left (fig. 184, A). 

 The thumb is very frequently 

 absent. In the Ruminants there 

 are only two fingers which are 

 functionally useful, these carry- 

 ing the hoofs. In all Ruminants, 

 however, there are two rudi- 

 mentary and functionally use- 



Fig. 184. -A, Fore-leg 'of the Horse: r leSS digits in addition. 



Radius ; c Carpus ; ca Canon-bone ; / Normally each digit has three 

 bphnt-bone ; a tirst phalanx or great - ' 111 



pastern;" Second phalanx or "small phalanges, CXCCpt the thumb, 



ti w - In the 



Radius; c Carpus ; ca Canon-bone ; s Whales and DolphmS 

 Supplementary toe. 



swimming-paddles, very like those of the Ichthyosaurus and 

 Pksiosaurus, the phalanges are considerably increased in 

 number as they are in those Reptiles. In all the Mammalia, 

 too, except the Cetacea, it is the rule that the terminal phalanx 

 in each digit should carry a nail, claw, or hoof. 



The power of opposing the thumb to the other digits of the 

 hand is found only in Man, and in a considerable number of 

 the Quadrumana, but never so perfectly developed as in Man. 

 In Man only does this power attain its full perfection, and it 

 constitutes one of the most striking of the merely anatomical 

 peculiarities by which Man is separated from the Monkeys. 



