Page 3 - LN-CH-16

Various parts of alimentary canal are discussed below
i. Mouth and Buccal Cavity
Mouth is a slit like opening, bounded by two soft, movable lips. It opens into a small
vestibule (space enclosed between lips and cheeks externally and gums and teeth
internally), which inturn leads into the buccal or oral cavity.
Oral cavity further comprises of two main components a. Teeth
These are hard structures present in the mouth on both the jaws (i.e., upper and
lower jaw). Each tooth is embedded in a socket of jaw bone.
Mammalian teeth are characterised by following three features
* Thecodont The teeth are fixed in sockets. They have very well-developed roots,
which are implanted deeply in the jaw bone socket.
* Diphyodont Like other mammals, human beings also has two sets of teeth formed
during lifetime. The first set of teeth is temporary and is known as milk or deciduous
teeth.
Milk teeth are 20 in number.
* The milk set is replaced by the second set known as permanent teeth or adult
teeth. Permanent teeth last for whole life, if lost, cannot be replaced.
* Heterodont An adult human has 32 permanent teeth, but they are of different size,
shape and type.
They are of following four types
* Incisors (I) for cutting of food
• Canine (C) for tearing the food
* Premolars (Pm)
* Molars (M) for crushing, grinding and chewing the food.