Page:Natural History, Birds.djvu/201

188 Climbers, possessing yoked toes, he remarks that the Parrots and the Woodpeckers are the only families whose toes are strictly and constantly disposed in pairs; the external toe of the other Scansores being retractile; and these latter are never seen to climb, at least to that extent which is common to the two families in question. "We may thus venture," he continues, "to separate the Parrots and Woodpeckers from the other Families, and to associate them together, in consequence of the affinity in these essential characteristics of the tribe. In this point of view they will compose its normal groups as Climbers par excellence; differing, however, as to the mode in which they climb; the Parrots using the foot chiefly in grasping the object, which assists them in their ascent, and in conjunction with the bill, while the Picidæ rely upon the strength and straightness of the hind toes, in supporting them in a perpendicular position on the sides of trees; in which posture they are also assisted by the strong shafts of the tail feathers. While I was influenced by these general points of coincidence in placing the Psittacidæ and Picidæ together, I recognised a group which appeared to intervene between them, and to diminish the apparent distance that exists even in the form of their bill. That important group which comprises the Linnaean Barbets, evidently exhibited the expected gradation in the structure of that member; the bill of Pogonias, ., approaching most nearly that of the Parrots, by its short, strong, and hooked conformation, while the straighter and more lengthened bill of the true Bucco united itself to that of Picus. Many other particulars in form, and also in