The Mouth

Digestive System of the Pig

The rima oris is extensive, the angles of the mouth being situated far back. The upper lip is thick and short, and is blended with the snout; the lower lip is small and pointed. The labial glands are few and small.

The mucous membrane of the cheeks is smooth. The buccal glands are compactly arranged in two rows opposite the cheek teeth. The parotid duct opens opposite the fourth or fifth cheek tooth.

The hard palate is long and narrow; it is marked by a median furrow, on each side of which are twenty or more ridges. On its anterior part there is a triangular incisive papilla, at which the naso-palatine ducts open.

The soft palate is very thick. Its direction almost continues that of the hard palate, i. e., it is nearly horizontal. It extends to the middle of the oral surface of the epiglottis. It has a median prolongation termed the uvula. The oral surface presents a median furrow, on either side of which is an oval raised area, marked by numerous crypts; these elevations are the tonsils. Tonsillar tissue also occurs in the lateral walls of the fauces.

The tongue is long and narrow and the apex is thin. Two or three vallate papillæ are present. The fungiform papillæ are small and are most numerous laterally. The filiform papillæ are soft and very small. On the root there are soft, long, pointed papillæ, directed backward. Foliate papillæ are also present.

There is a well-marked median glosso-epiglottic fold, on either side of which is a depression (Vallecula epiglottica). The frenum linguæ is double.

The dental formula of the pig is:

( 3 1 4 3 )

2 ( I

C

P

M

) = 44

( 3 1 4 3 )

The formula for the temporary teeth is:

( 3 1 4 )

2 ( Di

Dc

Dp

) = 32

( 3 1 4 )

The upper incisors are small; they are separated from each other by spaces, and from the canines by a larger interval. The first incisors are the largest, are convergent, and have no distinct neck. The second are narrower and somewhat smaller. The third (corner) incisors are much smaller, are flattened laterally, and have three small eminences on the crown.

The lower incisors are almost horizontal and are convergent and close together. The first and second are about equal in size, prismatic, and deeply implanted in the jaw. The labial surface is slightly convex, the lingual concave and marked near its extremity by a ridge. The third incisor is much smaller and has a short narrow crown and a distinct neck.

The canine teeth or tusks of the male are greatly developed and project out of the mouth. The upper canine of the boar may be about three or four inches (ca. 8 to 10 cm.) long. The crown is conical and is curved somewhat backward and outward; the embedded part is curved and has a large pulp cavity. The lower canine may reach a length of eight inches or more (ca. 20 cm.); the crown is prismatic and is curved backward and outward in front of the upper one, so that the friction between the two keeps a sharp edge on the lower tooth. In the sow they are much smaller.

The average periods of eruption of the teeth are given in the subjoined table.

Tooth Eruption Change

I1 2 to 4 weeks 12 months

I2 upper 2 to 3 months
lower 1½ to 2 month
16 to 20 months

I3 Before birth 8 to 10 months

C Before birth 9 to 10 months

P1 5 months

P2 5 to 7 weeks 12 to 15 months

P3 upper 4 to 8 days
lower 2 to 4 weeks.

P4 upper 4 to 8 days
lower 2 to 4 weeks

M1 4 to 6 months

M2 8 to 12 months

M3 18 to 20 months

The cheek teeth increase in size from before backward. They have (with certain exceptions noted below) complex tuberculate crowns; the term bunodont is applied to this condition, as distinguished from the selenodont structure in horses and cattle, in which there are prominent ridges of enamel. They are short-crowned teeth with a distinct neck and root. The first tooth in each jaw is small, simple, and appears only once; in the lower jaw it is near the canine, in the upper near the second cheek tooth. The next two teeth are larger, laterally compressed, and sectorial. The fourth tooth below is larger, but otherwise like the preceding ones, while the upper one is much wider and is tuberculate.

The parotid gland is large and triradiate. It extends very little on to the masseter muscle and its upper angle does not quite reach the base of the ear. It is pale in color, and is embedded in fat in animals in good condition. On its deep face are several large subparotid lymph glands, some of which are only partially covered by the parotid. The duct arises on the deep face, has a course similar to that of the ox, and perforates the cheek opposite the fourth or fifth upper cheek tooth. Small accessory glands (Glandulæ parotideæ accessoriæ) may be found along the course of the duct.

The submaxillary gland is small, reddish in color, and oval in outline; it is covered by the parotid. Its superficial face is convex, and is marked by rounded prominences. From its deep face a narrow process extends forward about two or three inches (ca. 5 to 7.5 cm.) beneath the mylo-hyoideus muscle along with the duct. The latter opens near the frenum linguæ, but there is no papilla.

The sublingual gland has an arrangement similar to that of the ox. The posterior part (Glandula sublingualis grandicanalaris) is reddish-yellow in color, and is about two inches (ca. 5 cm.) long, and half an inch wide; its posterior end is in relation to the submaxillary gland and its duct. The anterior part is much larger, being two or three inches (ca. 5 to 7 cm.) long and about twice the width and thickness of the posterior part. All or most of the ducts from the posterior part unite to form the ductus sublingualis major, which opens near the ductus submaxillaris. Eight or ten ductus sublinguales minores convey the secretion from the anterior part through the floor of the mouth.