MOUTH AND SALIVARY GLANDS. The mouth, in anatomy, is an oval cavity at the beginning of the alimentary canal in which the food is masticated. The opening is situated between the lips, and at rest its width reaches to the first premolar tooth on each side.
The lips are fleshy folds, surrounding the opening of the mouth, and are formed, from without inward, by skin, superficial fascia, orbicularis oris muscle, submucous tissue, containing numerous labial glands about the size of a small pea, and mucous membrane. In the deeper part of each lip lies the coronary artery, while in the mid-line is a reflection of the mucous membrane on to the gum forming the fraenum labii.
The cheeks f orm the sides of the mouth and are continuous with the lips, with which their structure is almost identical save that the buccinator muscle replaces the orbicularis oris and the buccal glands the labial. In the subcutaneous fascia is a distinct mass of fat, specially large in the infant, which is known as the sucking pad. On the buccal surface of the cheek, opposite the second upper molar tooth, is the papilla which marks the opening of the parotid duct, while, just behind, are four or five molar glands, larger than the buccal, the ducts of which open opposite the last molar tooth. The mucous membrane of the cheek, like that of the rest of the mouth, is of the stratified squamous variety (see EPITHELIUM) and is reflected on to the gums.
The gums consist of mucous membrane connected by thick fibrous tissue to the periosteum of the jaws. Round the base of the crown of each tooth the membrane rises to a little collar.
The roof of the mouth is concave transversely and antero posteriorly, and is formed by the hard and soft palate. The hard palate consists of mucous membrane continuous with that of the gums and bound to the periosteum of the palatine processes of the maxillae and palate bones by firm fibrous tissue. In the mid-line is a slight ridge, the palatine raphe, which ends in front in the pala tine papilla, marking the position of the anterior palatine canal. From the anterior part of the raphe five or six transverse ridges or rugae of the mucous membrane run outward. (For a descrip
tion of the soft palate see PHARYNX.) The floor of the mouth can only be seen when the tongue is raised, then the reflection of the mucous membrane from the gums to it is exposed. In the mid-line is a prominent fold (fraenum linguae), and on each side of this a sublingual papilla, on to the summit of which the duct of the submaxillary gland opens. Run ning outward and backward from this is a ridge (plica sublin gualis), which marks the upper edge of the sublingual gland, and on to which most of the ducts of that gland open. (For a descrip tion of the TONGUE and the TEETH see special articles.) Salivary Glands.—The salivary glands are the parotid, sub maxillary and sublingual, though the small scattered glands such as the labial, buccal, molar, lingual, etc., probably have a similar function.
The parotid gland is the largest, and is situated between the ear and the ramus of the mandible. In cross-section it is roughly tri angular, its outer wall or base being bounded by the parotid fascia, its anterior by the jaw, and its posterior by the mastoid process and sterno-mastoid muscle. Where the anterior and posterior walls meet to form the apex is the styloid process. Above the gland reaches to the zygoma, and below to the level of the angle of the jaw, where a strong process of the deep cervical fascia separates it from the submaxillary gland. The outline of the gland is ob scured by several processes, one of which, the facial lobe, runs forward, superficial to the masseter muscle, accompanying the duct; a separate part of this is called the socia parotidis. Others are pterygoid, pre-styloid and post-styloid, but all are very va riable. The facial nerve, the temporo-maxillary vein, and the ter mination of the external carotid artery, among other structures, are embedded in the gland. The parotid duct (Stensen's duct) crosses the upper part of the masseter and then pierces the bucci nator on its way to the mouth ; it is about tin. long.