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 



