292 THE ZOOLOGIST. 



therefore walks on the nails of four digits, one to each extremity, 

 and cattle, such as oxen and sheep, walk on the nails of eight 

 digits, two to each extremity. Such animals are said to be 

 Unguligradc. 



When we pass from Mammals to Birds we meet with a 

 great change of structure. Not only is the structure of both 

 the "hand" and the "foot" very different from anything 

 in beasts, but the difference between the " hand " and the 

 bird's " foot " in all birds is much greater than we find to 

 exist in almost any beast. The "hand" of the bird is in all 

 cases exclusively a locomotive organ, one for flight in the air, 

 except in such a bird as the Penguin, where it is for flight in the 

 water. The hand serves this locomotive purpose exclusively as 

 being a support for certain feathers, and consists at the most 

 of but three rudimentary, very short, fingers (the poUex, second 

 and third), the metacarpals of which have united together to 

 form a single bone. Thus the bony framework of the wing of 

 the bird is widely different from that of the wing of the Bat. 

 The carpus also is very small, and represented only by two 

 small bones, the other part having coalesced with the complex 

 metacarpal structure. 



When we proceed to consider the bird's foot, we find it also a 

 locomotive oi'gan, but occasionally, as in the Parrots, serving as 

 a prehensile organ, analogically— ?. c, according to functions — 

 something of a hand. The foot of the bird has always as many 

 as three digits, except in the Ostrich, where it has but two. It 

 has never more than four digits, that answering to one's little 

 toe being invariably absent. Generally the hallux is tiu'ned 

 backwards and the other three forwards, but occasionally, as in 

 the Swifts, all four may be turned forwards. Sometimes, as 

 in the Parrots and Trogons, they may be arranged in one of two 

 groups, two of the digits being opposed to two others. Thus the 

 hallux and fourth may be opposed to the second and third, as in 

 the Parrots ; or the hallux and second to the third and fourth, 

 as in the Trogons. As in mammals, so in birds, the hallux has 

 but two phalanges, and the second digit but three. Except in a 

 few birds [e.g., the Swifts and Goatsuckers), however, the third 

 digit has four phalanges, and the fourth has five. It is by this 

 we know that the two toes of the Ostrich consist of the fourth 

 and fifth digits. 



