Anatomy of the Cat

by Jacob Reighard; H. S. Jennings

—The mouth cavity extends from the lips to the pharynx. It is narrower toward the lips, broadens caudad as far back as the last teeth, then becomes narrowed to form the isthmus faucium, by which it communicates with the pharynx. The mouth cavity is divisible into the vestibule of the mouth (vestibulum oris), which comprises that part outside the jaws proper, bounded externally by the lips and cheeks, and the mouth cavity proper (cavum oris proprium), which lies within the teeth. That portion of the vestibule which is bounded by the cheeks is sometimes farther distinguished as the buccal cavity. The entire mouth cavity (except the teeth) is lined by the mucous membrane or mucosa.

The lips (labia oris) are thick folds of skin bounding the entrance to the mouth cavity. The outer surface is covered with hair; the inner surface is covered with the mucous membrane. The upper lip is marked in the median line by a deep external groove which extends upward to the septum of the nose. Along the inner surface of this groove the lip is closely united to the jaw by a thick fold, the frenulum of the upper lip. For some distance on each side of the frenulum the inner surface of the lip bears numerous large papillæ. The lower lip is also united to the jaw by a frenulum in the median line; it is again united to the jaw just caudad of the canine tooth, in the space between the latter and the first premolar. Caudad the two lips pass into each other (forming the commissura labiorum), and unite with the cheek. The muscles of the lips have been described ([page 105]).

The cheeks (buccæ) in the cat are comparatively thin and small, extending from the lips caudad to the ramus of the mandible. The outer surface is covered with hair; the inner surface is smooth and somewhat folded. The buccal cavity is rather small. On the inner surface of the cheek open the duct of the parotid (Steno’s duct), the ducts of the molar gland, and that of the infraorbital gland.

The roof of the mouth cavity is formed by the hard and soft palates. The hard palate (palatum durum) forms the cranial part of the roof; it is supported by the palatal plates of the maxillary and palatine bones. The mucosa of the hard palate is elevated to form seven or eight curved transverse ridges, which are concave caudad. Between the ridges are rows of papillæ. In front of the most cranial ridge is a papilla in the middle line, and at each side of the papilla is the opening of a small duct (the incisive duct or Stenson’s duct), which leads dorsad through the incisive foramen to the vomeronasal organ (or organ of Jacobson), which lies on the floor of the nasal cavity. Caudad of the hard palate the roof of the mouth is formed by the soft palate or velum palatinum, [described] below.

The floor of the mouth cavity is formed chiefly by the tongue, which extends as far caudad as the isthmus faucium. Ventrad of the free edge of the tongue the mucosa forms a prominent median vertical fold which unites the tongue with the floor of the mouth beneath it; this fold is the frenulum linguæ. On each side of the median line at the cranial border of the floor of the mouth is a prominent papilla, at the apex of which open the ducts of the submaxillary and sublingual glands, the former on the lateral side of the apex, the latter on the medial side.

The sides of the mouth cavity are formed by the teeth and the gums, covering the alveolar borders of the mandible, maxillaries, and premaxillaries.

The mouth cavity presents further for examination the glands, the teeth, the tongue, and the soft palate.

The Glands of the Mouth (Glandulæ oris).

—There are five pairs of salivary glands which open into the mouth cavity.

1. The parotid gland (glandula parotis) ([Fig. 65], 1; [Fig. 131], 10) is flattened, rather finely lobulated, and lies ventrad of the external auditory meatus and beneath the dermal muscles. Its cranial border follows the caudal border of the masseter muscle and overlies it somewhat; its caudal border is about three centimeters caudad of the border of the masseter. Its borders are unevenly lobed. The parotid duct (ductus parotideus: frequently called Stenon’s or Steno’s duct) is formed by the union of several smaller ducts near the ventral end of the cranial border of the gland. It passes craniad imbedded in the fascia covering the masseter. At the cranial border of the masseter it turns inward and lies close against the mucous membrane of the mouth, so that from the inside of the mouth it appears as a white ridge on the mucosa. It opens on the inside of the cheek opposite the most prominent cusp of the last premolar tooth. Along the course of the parotid duct in some cases one or more small accessory parotid glands are found.