“The Comparative Anatomy of Eating”, by Milton R. Mills, M.D.

Facial Muscles
CARNIVORE: Reduced to allow wide mouth gape

OMNIVORE: Reduced
HERBIVORE: Well-developed
HUMAN: Well-developed

Jaw Type
CARNIVORE: Angle not expanded

OMNIVORE: Angle not expanded
HERBIVORE: Expanded angle
HUMAN: Expanded angle

Jaw Joint Location
CARNIVORE: On same plane as molar teeth 

OMNIVORE: On same plane as molar teeth
HERBIVORE: Above the plane of the molars
HUMAN: Above the plane of the molars

Jaw Motion
CARNIVORE: Shearing; minimal side-to-side motion
OMNIVORE: Shearing; minimal side-to-side
HERBIVORE: No shear; good side-to-side, front-to-back 
HUMAN: No shear; good side-to-side, front-to-back

Major Jaw Muscles
CARNIVORE: Temporalis

OMNIVORE: Temporalis
HERBIVORE: Masseter and pterygoids 
HUMAN: Masseter and pterygoids

Mouth Opening vs. Head Size
CARNIVORE: Large

OMNIVORE: Large
HERBIVORE: Small
HUMAN: Small

Teeth: Incisors
CARNIVORE: Short and pointed

OMNIVORE: Short and pointed
HERBIVORE: Broad, flattened and spade shaped
HUMAN: Broad, flattened and spade shaped

Teeth: Canines 
CARNIVORE: Long, sharp and curved
OMNIVORE: Long, sharp and curved
HERBIVORE: Dull and short or long (for defense), or none
HUMAN: Short and blunted

Teeth: Molars
CARNIVORE: Sharp, jagged and blade shaped 
OMNIVORE: Sharp blades and/or flattened
HERBIVORE: Flattened with cusps vs complex surface
HUMAN: Flattened with nodular cusps

Chewing
CARNIVORE: None; swallows food whole

OMNIVORE: Swallows food whole and/or simple crushing
HERBIVORE: Extensive chewing necessary
HUMAN: Extensive chewing necessary

Saliva
CARNIVORE: No digestive enzymes

OMNIVORE: No digestive enzymes
HERBIVORE: Carbohydrate digesting enzymes
HUMAN: Carbohydrate digesting enzymes

Stomach Type
CARNIVORE: Simple

OMNIVORE: Simple
HERBIVORE: Simple or multiple chambers
HUMAN: Simple

Stomach Acidity
CARNIVORE: Less than or equal to pH 1 with food in stomach 

OMNIVORE: Less than or equal to pH 1 with food in stomach
HERBIVORE: pH 4 to 5 with food in stomach
HUMAN: pH 4 to 5 with food in stomach

Stomach Capacity
CARNIVORE: 60% to 70% of total volume of digestive tract 
OMNIVORE: 60% to 70% of total volume of digestive tract
HERBIVORE: Less than 30% of total volume of digestive tract
HUMAN: 21% to 27% of total volume of digestive tract

Length of Small Intestine
CARNIVORE: 3 to 6 times body length

OMNIVORE: 4 to 6 times body length
HERBIVORE: 10 to more than 12 times body length
HUMAN: 10 to 11 times body length

Colon
CARNIVORE: Simple, short and smooth

OMNIVORE: Simple, short and smooth
HERBIVORE: Long, complex; may be sacculated
HUMAN: Long, sacculated

Liver
CARNIVORE: Can detoxify vitamin A 

OMNIVORE: Can detoxify vitamin A
HERBIVORE: Cannot detoxify vitamin A
HUMAN: Cannot detoxify vitamin A

Kidney
CARNIVORE: Extremely concentrated urine

OMNIVORE: Extremely concentrated urine
HERBIVORE: Moderately concentrated urine 
HUMAN: Moderately concentrated urine

Nails
CARNIVORE: Sharp claws

OMNIVORE: Sharp claws 
HERBIVORE: Flattened nails or blunt hooves
HUMAN: Flattened nails

The Natural Human Diet

According to biologists and anthropologists who study our anatomy and our evolutionary history, humans are herbivores who are not well suited to eating meat.

Unlike natural carnivores, we are physically and psychologically unable to rip animals limb from limb and eat and digest their raw flesh. Even cooked meat is likely to cause human beings, but not natural carnivores, to suffer from food poisoning, heart disease, and other ailments.

People who pride themselves on being part of the human hunter tradition should take a second look at the story of human evolution. Prehistoric evidence indicates that humans developed hunting skills relatively recently and that most of our short, meat-eating past was spent scavenging and eating almost anything in order to survive; even then, meat was a tiny part of our caloric intake.

Humans lack both the physical characteristics of carnivores and the instinct that drives them to kill animals and devour their raw carcasses. Ask yourself: When you see dead animals on the side of the road, are you tempted to stop for a snack? Does the sight of a dead bird make you salivate? Do you daydream about killing cows with your bare hands and eating them raw? If you answered “no” to all of these questions, congratulations—you’re a normal human herbivore—like it or not. Humans are simply not designed to eat meat.

(statement from:  http://www.goveg.com/naturalhumandiet.asp)