SOME ACCESSORIES 155 
He has a temperature considerably higher than that 
of a human being ; in some species it ranges up to 
111° F., or even just over that. In fact his vitality 
is very great, and all his physiological processes are 
brisk and vigorous. It would not do, therefore, to 
economise in fuel. Though his fore limbs have been 
metamorphosed into wings and are incapable of 
doing the work of hands, his beak at the end of his 
long, supple neck (for it is of some length even in a 
comparatively short-necked bird) is quite equal to 
the task, and picks up big and small things easily 
and with skill. Moreover, birds of prey use their 
feet as hands, and most effectively too. As soon 
as he has seized his food, the bird sends it post-haste 
to his crop, or, if he is cropless, to his stomach, his 
proventriculus, to be digested. He has nothing cor- 
responding to the apparatus that makes breathing 
easy for us while we chew our food. Nor has he 
any teeth; powerful teeth could only exist if his 
jaws were strong and heavy, and it is important 
that his head should be light, for a heavy head would 
make fore-and aft balance difficult during flight. 
Digestion is rapid. In the case of a seed-eater, after 
the digestive juices have operated on the food in the 
proventriculus, it passes to the gizzard, to be ground 
up in that powerful mill. There seems to be no 
period of torpor after a meal as there is with a reptile, 
though the actual weight of what is swallowed may 
make flight difficult. 
Circulation, Breathing, Temperature. 
The heart is very efficient. Like the mammalian 
heart, it has four chambers, with an impassable wall 
