Humans do not have microflora that can hydrolyze cellulose, but plant-eating herbivores do. One advantage of that though is that the cellulose helps move food through your gut and aids digestion. Herbivores have fermentation chambers in their alimentary canals that contain mutualistic bacteria and protists that can break down the cellulose for them; some of the microorganisms also use some of the sugars from the digested cellulose to produce nutrients vital to the animal, such as vitamins and amino acids. Also, herbivores have longer alimentary canals relative to their body size, due to the fact that plant matter is harder to digest because of the cell walls.
Here is an excerpt on herbivore teeth structure, taken from Campbell Biology, 10th Edition.
"Herbivores, such as horse and deer, usually have premolars and molars with broad ridged surfaces that grind through tough plant material. The incisors and canines are generally modified for biting off pieces of vegetation. In some herbivores, canines are absent" (Reece et al. 906).
- Reece, Urry, Cain, Wasserman, Minorsky, and Jackson. Campbell Biology. 10th ed. N.p.: Pearson, 2014. Print.