SOUR CROP
MILDRED

The crop is the hen's handbag, she gathers feed through the day and stashes it in there where the first part of digestion takes place. It is located to the right hand side (left to you) of her keel bone about 4 inches below her head! So on Miss Fleur pictured below it is clearly visible on her right side, next to her neck skeleton, which is so apparent because she was almost starved to death in the cages.
Click here to watch this video is part of The Virtual Chicken education material and is really useful to aid understanding of a hen's digestive process.
So now you will see that a hen's internal workings are really quire amazing and to be in optimal health requires a good clean, sensible diet - appropriate for hens! Some people think hens are dustbins and will eat all sorts of anything! This is an old fashioned notion and back in the day when 1) hens hadn't been genetically modified to prioritise egg laying over bodily health and 2) the general diet of the population was a lot simpler and less processed, this may well have been acceptable. Now I believe it is not acceptable and can lead to digestive and health issues for your hens.