Gross Anatomy of the Digestive System


Mammals eat a wide variety of foods. Some are herbivorous and eat manly plant material. Some are carnivorous and eat mainly meat. Omnivorous mammals eat a mixture of meat and plant material. Many changes in the mammalian skull are related to variations in feeding. Adaptations for feeding among mammals are clearly demonstrated by different patterns of dentition both in numbers and shapes of teeth. Numbers of teeth in mammals are usually indicated by giving a dental formula. Mammals have four types of teeth: incisors, canines, premolars and molars. Incisors are chisel-shaped and generally used for holding, biting, gnawing, shearing, etc. Canines are sharp and conical in shape and are used for stabbing and ripping during feeding or fighting. Premolars and molars are used to grind or break up food. Premolars differ from molars in that they have fewer roots and are often simpler in form. A dental formula which indicates the number of each type of tooth is given as follows:



The four numbers in the top row give the number of each type of tooth in on side of the upper jaw, while the lower set gives the number of each type in one half of the lower jaw. From left to right, the numbers represent incisors, canines, premolars, and molars. Thus, the animal represented above has two incisors, one canine, two premolars and three molars in each half of its upper jaw and in each half of its lower jaw. How many teeth does it have in its entire mouth?

Determine the dental formula for the skulls shown on the right. The teeth are labeled in the higher magnification images. If teeth are missing, count the alveoli or sockets where the teeth were anchored. In some cases you may not be able to distinguish premolars from molars; for these skulls, write a formula using only three types of teeth (incisors, canines, cheek teeth). An example of a formula combining premolars and molars would be:



Notice that many herbivorous animals lose the canine teeth and develop a diastema, or gap between the incisors and the premolars. What function do you think loss of the canine and development of the diastema serves?

The shape of teeth also varies depending on what an animal eats. Herbivorous mammals tend to have flattened premolars and molars to grind u plant material, and their incisors are specialized for biting off grass and leaves. Carnivorous mammals have canines for stabbing and tearing, and premolars and molars specialized for shearing off bites of meat. The number of premolars and molars is often reduced. The incisors are adapted for biting and holding. Mammals that primarily eat insects tend to have teeth with sharp points to pierce the exoskeleton. Gnawing mammals have large, ever-growing, chisel-shaped incisors and grinding cheek teeth. Can you give an example of mammal with each type of dentition?

Examine the human tooth display to determine its dental formula.