HANDS AND FEET. 293 



The metatarsals of the foot are yet more consolidated than are 

 the metacarpals of the hand ; they form a sort of " cannon 

 bone," like those of the Jerboa before described. Moreover, not 

 only do they unite together, but with part of the tarsus also, the 

 rest of the tarsus being similarly united to the lower end of the 

 leg-bone. Thus in birds the foot does not move on the leg, as 

 in us and in beasts, but one part of the foot moves on another, 

 the joint between the foot and the leg being constructed in the 

 middle of the tarsus. 



In Eeptiles the hand has generally five long movable 

 digits, but they may be enclosed in a sort of fin, as in the Turtle ; 

 or greatly shortened, like those of the thick stumpy hand of the 

 Tortoise. The phalanges of the five digits are generally 2, 3, 4, 

 4, 3, or 2, 3, 4, 6, 3 in number. In the foot their number is like 

 that of birds, 2, 3, 4, 5, and the fifth digit (always absent in 

 birds) has in Lizards four phalanges. Earely, as in the 

 Chameleons, the digits of both hand and foot are arranged in 

 two bundles, opposed the one bundle to the other. Thus in 

 the hand, the first, second, and third digits are opposed to the 

 fourth and fifth, and in the foot the first and second digits are 

 opposed to the third, fourth, and fifth. 



In certain extinct reptiles — Pterodactyles— the hands were 

 to a certain extent modified, like those of existing Bats, to sup- 

 port a flying membrane or wing. In these rej)tiles, however, 

 instead of all the digits, except the pollex, being elongated, it 

 was only the outermost one which was so. In other extinct 

 reptiles, namely. Ichthyosauri and Plesiosauri, we have evidence 

 of certain conditions of limb which are full of interest. The 

 resemblance between our arm and leg and hand and foot are 

 almost as manifest as their differences. The number of primary 

 divisions of each, and the numerical difl'erence of the phalanges 

 of the innermost digits and of the other digits in each case, has 

 been already mentioned. In many animals the difiference be- 

 tween the hand and the foot is greater than in ourselves, but in 

 others it is much less. In none is it so .little as in IchtJiyosauri 

 and Plesiosauri, where the leg and foot is the i^erfect rejDetition 

 behind of the arm and hand in front. 



In the Ichthyosaurus the number of phalanges is greatly 

 increased, but that we have met with already in Cetaceans, which 

 seem to have been anticipated in the deep by their reptilian 



