Omasum

Different ruminants have different omasum structures and function based on the food that they eat and how they developed through evolution.

[4] The omasum is spherical[5] to crescent shape[6] and has multiple leaflets similar to that of a book[7] called omasal laminae.

[4] The omasal laminae are made of thin muscular layers covered with a nonglandular mucous membrane.

[5][2] In ruminants with a more sophisticated omasum[example needed], the large surface area[9] allows it to play a key role in the absorption of water, electrolytes,[2][4] volatile fatty acids, minerals, and the fermentation of food.

[2] The omasum is not only bigger in grass and roughage eaters but there is greater differentiation in the book-like structure; seen as an increase in the number of laminae.