174 TROPICAL WILD LIFE IN BRITISH GUIANA 



finger pointed down and inward, lying closely apposed to 

 the wing, and well out of liarni's way. They were sheathed, 

 as it were, between wing and body. The movement of exten- 

 sion caused the claws to be released and at the same time to 

 revolve in a fidl quarter of a circle, pointing thus directly for- 

 ward and inward. This becomes of dominant significance 

 when we recall the position of the claws in the fossil speci- 

 mens of Archaeopteryx. Recently, when reviewing the char- 

 acters of this wonderful creature with a view to restoration, 

 I was in great doubt about accounting for the position of the 

 claws in the partly spread wing. It seemed almost as if the 

 forward, inward pointing claws had been accidently crushed 

 into that position by pressure after the bird's death, or by 

 some flexure of the muscles and tendons after decomposition. 

 But when I saw the automatic rotation of the claws in the 

 young hoatzin as its wing spread, I realized that the condi- 

 tions were identical in the two forms, and that the unusual 

 posture of the claws in Archaeopteryx was, after all, quite 

 normal. It is a position wholly unlike that in the wing claws 

 of any other bird. The twist occurs chiefly in the phalangial 

 joint, but partly as well in the basal joint of the thumb. 



I was surprised to learn how exclusively arboreal were 

 these nestling hoatzins. I once saw an adult bird alight on 

 the ground, but rather from inability to fly farther than of 

 its own intention. When Schomburgk, in the third volume 

 of his JReiscn in Britisch Guiana, writes that he saw a flock 

 of several hundred which "chased each other from branch to 

 branch, while others ran about upon the ground," he was 

 either romancing or else confused these birds with trumpet- 

 ers. They do not run nor even walk upon the ground. 



My young hoatzins were as helpless as seals on solid 

 ground, their toes crumpling up and their feet practically 

 useless for progression. In attempting to go ahead the bird 

 fell forward, extended its wings wide and clawed vigorously 

 at the ground, pulling itself awkwardly along, while the feet 



