In the second order of birds, the perchers (_Passeres_ of Linnæus), which comprehends sparrows, thrushes, larks, &c., the foot is constructed for another and a very different purpose. Its chief office is to support the bird in a horizontal position upon the boughs and branches of trees and shrubs; hence the foot is long, the toes slender, very flexible, and armed with long, straight, weak claws, which are not at all retractile. All the birds of this order possess four toes, one of which, the hind toe (_hallux_), is placed straight out behind, the others being in front, and those situated externally are connected to the middle ones at their bases. The scales covering the foot are regularly disposed, and as they are not needed for the purpose of defence, they are thin and tender, resembling ordinary scarf skin. Even in the shrikes,—the birds of prey of this order, who feed upon living creatures and use the foot for securing them, the claws are not sharp, nor is the foot formed in such a manner as to ensure a very secure grasp, and we accordingly find that they merely press this organ upon their prey for the purpose of holding it. In a few other families of this order, as the todies, the kingfishers, &c., the foot is called upon to assist in feeding, and we consequently find certain modifications of structure indicative of this office. In order to strengthen the foot and to secure a firmer grasp, the external and middle toes are united almost to the apex, and the strength of the hind toe is considerably increased. In the third order, the climbers (_Scansores_), or, as they have been sometimes termed, the yoke-footed, to which the woodpecker and the parrot tribe belong, the structure of the foot is modified for the important purpose of enabling the creature to support itself in all positions upon the stems and branches of trees. In order to effect this the foot is made strong, short, and muscular, the claws sharp and curved, and the toes are placed in a very different position to that which they occupy in other orders, two of them being situated in front and two behind. By such a disposition, a strong, secure grasp is afforded; and thus it is that most birds belonging to this order are enabled to climb in a vertical position, and to effect movements like animals of the monkey tribe. In general these birds move very awkwardly upon a level surface, but in one or two species the structure of the foot is so modified that they can run upon the ground with great speed. This is the case with the travellers’ friend of South America, and with the ground parrot of New South Wales; and these creatures have accordingly slender toes so constructed, that one of the two placed behind can be brought in front at will, so that a larger and more secure basis of support is thus afforded.