feathers		similar to the internal cross bracing found in bones
back		birds inhale and exhale ? to move each breath
sweat		birds are designed for quick ?
sacs		Birds are designed for quick ?, thereby keeping them light
avain		Birds will sometimes swallow ? to help with digestion
larger		Birds eat a lot because they need a lot of ? to fly
humerus		a place which stores and moistens the bird's food
pectorals		deliver oxygen-rich blood to the bird's muscles
major		many bird bones are ?
keratin		grinds the bird's food to make it more easily digested
thin		plumage
girders		birds do not have ? glands in their respiratory system
sand		air ? collect the air that the birds breathe
muscles		birds have air ?, that are like tiny tubes in which air flows thru
energy		birds don't have strong ? muscles
hollow		most powerful bird muscles
arteries		pertaining to birds
excretion		skull bones of birds are very ?
capillaries		delivers oxygen-poor blood to the heart
sternum		without these powerful things, birds couldn't fly
gizzard		breastbone of bird, similar to a ship's keel
digestion		Pectoralis ? muscles lowers the bird's wings in flight
crop		a tendon is attached to the Pect. minor and ?, which raises bird's wings
veins		this along with struts of bone, makes up bird's bill
twice		bird's hearts are much ? in relation to its body size