Here is a pdf from www.uspoultry.org
I know the ceca is a part of the digestive tract that holds organisms that are very suited to aid in the digestion of Celulose and other materials that are difficult to digest. At least that is what I know of Horse digestion Horses have one so its called a Cecum... chickens have two so they are called Ceca
I hope this helps
Oh and an interesting note. Chickens dont have a bladder. So their urine is excreted as a white past that sits ontop of the poo.
And every few Poops there will be one that is called a Cecal poop. Cecal poops should be lose a bit watery and very stinky. Sometims you will see other chickens seek out that Cecal poop and eat a bit of it.... I know Ewww . But even with horses they do this periodically to reinoculate their own digestive process.