THE MOUTH
Since cattle do not ingest large mouthfuls, the small size of the oral opening is no disadvantage to the animal; however, it is a considerable hindrance to clinical inspection of the mouth parts and pharynx.
The vestibule between the cheeks and the margin of the jaws is surprisingly roomy; the inner surface of the lips and cheeks bears large, backward-pointing papillae that are most prominent toward the corners of the mouth (Figure 25-13/5).The mouth cavity proper is long and narrow and is largely occupied by the tongue. The hard palate is most constricted directly in front of the cheek teeth. It is sculpted to display a dozen or more transverse ridges that progressively decrease in prominence and at last
Figure 25-14 The roof of the bovine oral cavity. 1, Incisive papilla; 2, dental pad; 3, buccal papillae; 4, palatine ridges; 5, palatine raphe; 6, first upper cheek tooth (P2).
fade out toward the back of the mouth; their crests carry numerous papillae (Figure 25-14). The region occupied in other species by the upper incisor teeth here carries the paired dental pads; these are crescentic elevations that are pliant when compressed, though cornified on the surface (Figure 25-14/2). Cattle do not graze by edge-to-edge biting but, after drawing a tuft into the mouth with the assistance of the tongue, sever it by pressing the incisor blades against these pads; the risk of injury to the pads is reduced by their tough covering and pliant consistency and by the procumbent arrangement and rather loose implantation of the incisors (Figures 25-15 and 25-16). The incisive papilla behind the pads is flanked by the small openings of the incisive ducts.
The lips of small ruminants are much more mobile than those of cattle. They are the principal organs of prehension and enable these species to crop a pasture closely.
In cattle it is the pointed tongue that is the principal organ of prehension. Its caudal part is raised to form a large torus that is marked off in front by a transverse lingual fossa in which food tends to collect; it is a potential portal for infection because the epithelium, quite delicate within the fossa, is easily pricked by sharp particles (Figure 25-17/5). The papillae that give the surface of the tongue a characteristic roughness are concentrated over the dorsum and toward the apex. Harsh,
Figure 25-15 Front view of the incisors of a 2-year-old cow. The central incisors are permanent, the others deciduous.
Figure 25-16 Front view of the incisors of a 4¼- to 5-year- old cow. The fourth incisors have reached the height of their neighbors and are coming into wear.
caudally directed, filiform papillae are freely spread over the apex, while flat and conical lenticular papillae are present on the torus (Figure 25-17/4',4"); all of these have a purely mechanical function. As usual, it is the fungiform papillae scattered on the apex and the numerous vallate papillae (Figure 25-17/3) present toward the root that carry the sensory receptors concerned with taste. An accumulation of lymphoid tissue toward the root constitutes the diffuse lingual tonsil.
The oral floor below the apex of the tongue presents a fleshy sublingual caruncle to each side; the ducts of the mandibular and monostomatic sublingual glands open beside this (see Figure 25-13).
The orientation of the projections on the cheeks, palate, and tongue encourages the backward movement of material within the mouth; this, combined with the general insensitivity of the mouth parts and the copious salivary secretion, may explain the frequency with which cattle swallow foreign bodies concealed within their forage.
Figure 25-17 Bovine tongue and lower jaw. 1, Soft palate, cut; 2, palatoglossal arch; 3, vallate papillae; 4, filiform papillae; 4', lenticular; 4", conical; 5, lingual fossa; 6, buccal papillae; 7, first lower cheek tooth (P2); 8, M1.