(1) Mouth and Buccopharyngeal Cavity - Mouth is a horizontal transverse slit like aperture which is surrounded by upper and lower lip, a specific muscle is associated with lip called ''orbicularis oris'' muscle.
# Serous glands are found on inner part of lip. Serous glands is modification of muscle gland.
# Mouth opens into buccopharyngeal cavity, this is divided into two parts-

A. Buccal Vestibule - The space between the gums and cheeks where food is stored temorarily for some time. It is a peripheral part.
B. Main oral cavity - It is inner and central part which is surrounded by upper and lower jaw, lined by stratified squamous epithilium.

Palate is differentiated into two parts :

1. Hard Palate -
# It is the anterior part of palate. It is made up of maxilla and palatine bone in human.
# On the ventral surface of hard palate, some projection or transverse ridges are present which are called as palatine rugae.
These rugae prevent slip out of the food from buccal cavity during mastication, these rugae are well developed in carnivorous animals.

2. Soft Palate -
# It is the posterior part of palate. It is made up of involuntary muscle fibrous connective tissues and mucous epithelium.( stratified squamous epithelium)
# The posterior out growth of soft palate which hangs down in the form of finger like process called as Uvula or Velum palati. On the dorsal side of Uvula, internal nasal pores are present.
# Uvula or Velum palati covers the opening of internal nasal pores during ingestion of food, so food particle can not move inside nasal chamber.
# Soft palate is situated in pharynx and is divided into two parts. Upper part of pharynx is called Nasopharynx which is relate to nasal chamber. The lower part of pharynx is called oropharynx which is related to oral cavity. One pair of opening
of Eustachian tube is present in the nasopharynx. This Eustachian tube is related to the middle ear. It maintain air pressure.

Pharynx is common path for air and food.

# On the floor of oral cavity a mascular flat, fleshy plate like structure is present which is called tongue. The anterior part of tongue is free while posterior part of tongue is connected to hyoid bone.
# The ventral surface of tongue is connected to floor of buccal cavity through a very flexible membrane/ ligamentous fold called as "frenulum linguae"

On the dorsal surface of tongue, it is divided into two unequal parts by a V shaped sulcus, called as sulcus terminalis.
It is divided into two parts -
(a) Pharyngeal part - It is the posterior 1/3 part of the tongue.
(b) Oral or papillary part - It is anterior 2/3 part of tongue.

MUSCLES OF TONGUE :

Extrinsic muscle :- It is found on outer and superficial part of tongue. It helps in outward and inward movement of tongue.
Intrinsic muscle :- It is situated in the deep part of tongue. It helps in the change of shape of tongue.

PAPILLAE :
Three types of functional papillae are found in this part in which gustatory or taste receptors are present in the form of test buds.

1. Fungiform Papillae -
It is pink coloured, small and spherical in shape. It is found on the entire surface of tongue but mostly present at the anterior part of tongue. It is attached to tongue with the help of small pedicle. It provides pink colour to the tongue.

2. Filliform papillae (Conical papillae) - They are thread like, white coloured and conical in shape. They are also fiind on entire surface of tongue. They are most numerous but devoid of taste buds.

3. Circumvallate papillae - It is the largest and least existed papillae (8-12), they are large spherical shape papillae which are found near to sulcus terminalis.

Foliate papillae - They are found on the mid lateral surface of tongue. They are vestigeal in human.

Function of tongue : Reception of taste.