In the fowl the lips and cheeks are replaced by the beak - an area of dense and horny skin lying over the mandible and incisive bones that serve as the bony foundation. There are no teeth. The so called egg tooth found on the end of the beak of newly hatched chickens is an aid to their escape from the egg at hatching and disappears after a day or two. The hard palate, forming the roof of the mouth, presents a long, narrow median slit that communicates with the nasal cavity (median - along the middle). The hard palate has five transverse rows of backwardly pointing, hard, conical papillae. Numerous ducts of the salivary glands pierce the hard palate to release their secretions into the mouth cavity.
Salivary glands
A thick layer of stratified squamous epithelium covers the free surface. The salivary glands run the whole length of the hard palate, the groups of glands merging to form one mass of glandular tissue under the epithelium. Lymphoid tissue is found in most glands.
The salivary glands are:
1. Maxillary - in the roof of the mouth
2. Palatine - on either side of the nasal opening in the roof of the mouth
3. Apheno-pteryoid glands - in the roof of the pharynx on each side of the common opening for the eustachian tubes (the eustachian tubes connect the middle ear to the mouth and their function is to equalise the air pressure on each side of the tympanic membrane in the ear)
4. Anterior sub-mandible glands - in the angle formed by the union of the upper and lower beaks or mandibles
5. Posterior sub-mandibular glands
6. Lingual glands - in the tongue
7. Crico-arytenoid glands - around the glottis
8. A small gland in the angle of the mouth
Pharaynx and tongue
The pharynx is continuous with or follows the mouth. The combined cavity of the mouth and the pharynx is often referred to as the oropharynx. The common opening for the two eustachian tubes is located in the middle of its dorsal wall (roof). The tongue is long and pointed and conforms to the shape of the beak in which it operates. The epithelium of the tongue is thick and horny, especially towards the tip. A transverse row of simple, large and horny papillae with their tips directed towards the rear of the mouth cavity are located on the posterior end. The hyoid bone provides the framework to support the tongue. The entoglossal bone extends longitudinally in the median plane. small patches of lymphatic tissue are located throughout the corium. Mucous glands are located in the tongue with short ducts directed towards the rear. Some but not others believe that there are taste buds located on the tongue. In any case the sense of taste appears to be very weak if at all present.
The mouth has two major functions:
1. To pick up the food particles - this skill is modified by beak trimming. Birds with normal beaks become very adept at the manipulation of food particles thus leading to significant food wastage and one effect of beak trimming is to reduce this wastage.
2. To direct the food into the oesophagus - as part of the bird’s eating behaviour.
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