Along with the sense of taste there are other senses in the mouth which play an important part, such as pressure and the sense of heat and cold, and it is often hard to distinguish them from the pure sensation of taste, which indeed is always accompanied by them.
Salivary Glands.—On either side of the mouth are three racemose glands for the secretion of the saliva, which serves to soften and lubricate the food and partially to digest starches by means of its ferment, ptyalin. The [parotid gland] is the largest and is below and in front of the ear, opening by Stensen’s duct. The [submaxillary gland] is below the jaw toward the back on either side and its duct is Wharton’s duct. The [sublingual gland] lies beneath the mucous membrane of the floor of the mouth and opens by eight to twenty tiny ducts beside the frenum, the ducts of Rivinus. The activity of the glands depends upon the blood supply; the more blood the greater their activity.
Fig. 20.—Dissection of the side of the face, showing the salivary glands: a, Sublingual gland; b, submaxillary gland, with its duct opening on the floor of the mouth beneath the tongue at d; c, parotid gland and its duct, which opens on the inner side of the cheek. (After Yeo.)
The Tonsils.—The tonsils vary in size and in tonsillitis swell and may even meet in the median line. They are frequently removed. When they are enlarged one often gets a third tonsil or adenoids, a lymphoid growth at the back of the pharynx which causes mouth-breathing by day and snoring by night. A child with adenoids is starved for air and what air is breathed in is not warmed. The growth should be removed.
A short frenum produces tongue-tie, which may be remedied by snipping. Cancer of the tongue is fairly common and necessitates a radical operation. In mumps the parotid glands are inflamed and enlarged.
The Ear.—The special organ of hearing is the ear, to which there are three parts, the external, the middle, and the internal ear.
The external ear consists of the pinna or expanded cartilaginous portion, for the concentration and direction of sound waves, and the external auditory canal, partly cartilage, partly bone, which is directed forward, inward, and downward and conveys sound to the middle ear.
Fig. 21.—The small bones of the ear; external view (enlarged).
(After Gray.)