HOW A-BIRD GOES TQ BED. 15( 
specially adapted to this habit by having a callous 
bare notch in its breast (and breastbone) which fits 
snugly over a small branch. Many mammals, as 
camels, etc., have similar callosities (bare, hard places) 
to lie upon, but this is the only bird that “takes up 
its bed and walks.” This squatting position is espe- 
cially helpful to birds in automatically clasping the 
limb when asleep, since these tendons in running 
around the outside of the (then) Z-shaped legs are in- 
cidentally tightened by it. 
7 It has been usual to note that birds have a special 
muscle (the ambiens) whose sole purpose is to so au- 
tomatically render the 
toes clasping. But 
since it flexes the in- 
ner and middle toes 
only and has no effect 
upon the hind toe, its 
use in connection with 
roosting is not strik- 
ing. Since it is not 
found at all in the A fieldfare. 
true perchers (?as- 
seres) and is found largely in low birds, many of 
which do not perch, it likely has (or has had) more 
to do with swimming than perching. 
Picarian birds, which nest so largely in holes, are 
apt to roost there; but it does not always follow, as 
has been broadly asserted (Burroughs), that a bird al- 
ways roosts in the same kind of place in which it nests. 
This is contradicted in turkeys, Western quails, house 

