that connect the Orders and Families of Birds. 455 
are strictly and constantly disposed in pairs : and they are con- 
sequently the only groups which constantly benefit by that con- 
struction in climbing. ‘The external hind toe of the other Scan- 
sores is retractile : and these birds are never observed to climb, at 
least to that extent which is common to the two families in ques- 
tion. We may thus venture, I think, to separate the Parrots and 
Woodpeckers from the other families, and to associate them toge- 
ther, in consequence of their affinity in these essential characteris- 
tics of the tribe. In this point of view they will compose its normal 
groups, as climbers par eacellence, 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 Picide rely upon the strength 
and straightness of the hind toes in supporting them in a per- 
pendicular 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 Psittacide and Picide together*, I recognised a group which 
appeared to intervene between them, and to diminish the appa- 
rent distance that exists even in the form of their bill. That im- 
portant group, which comprises the Linnean Barbets, evidently 
exhibited the expected gradation in the structure of that mem- 
ber; the bill of Pogonias, lll. approaching most nearly that of 
the Parrots, by its short, strong, and hooked conformation‘, 
* There are some minuter and less essential points also in which this approxima- 
tion is evident. Some of the Psittacide, among which I shall particularize the Psit- 
tacus Alexandri, Linn., and its congeners, partially employ the tail in supporting 
themselves as they climb, in a corresponding manner with the Woodpeckers. I make 
this remark from my own observation. The tongue also peculiar to the family may be 
observed to become slenderer, and, as is said, more extensible, in that group of which 
P. aterrimus, Gmel. is the representative; thus evincing an approximation, slight in- 
deed, but still an approximation, to the biil of the Woodpeckers. 
+ It also comes nearer to them by its frugivorous habits. ‘ [ls (Sc. les Barbicans) 
mangent plus de fruits que les autres espéces.”—Cuv. Regne Anim. i. p. 428. hil 
whiie 
