The size and form of the mouth vary greatly in different breeds, the
cavity being in some long and narrow, in others short and wide. The
=rima oris= is very extensive, so that the labial commissure is opposite
the third or fourth cheek tooth. The =lips= are thin and mobile, and
present numerous tactile hairs. The upper lip has a small, central, bare
area which forms part of the muzzle, and is marked by a central groove,
the philtrum, or (as in the bulldog) a fissure, giving the appearance of
harelip. The lateral borders of the lower lip are flaccid and
denticulated. The mucous membrane is usually pigmented and forms
distinct frena labiorum. The labial glands are small and scanty.
[Illustration:
FIG. 326.—TONGUE OF DOG. _a_, Tonsil; _b_, vallate papillæ; _c_,
foliate papilla; _d_, fungiform papillæ; _e_, median groove of
dorsum; _f_, epiglottis; _g_, soft papillæ of root; _h_, middle
glosso-epiglottic fold; _1_, tip; _2_, root. (Ellenberger-Baum,
Anat. d. Haustiere.)
]
The =cheeks= are loose and capacious, and their mucous lining is smooth
and more or less pigmented. The =parotid duct= opens usually opposite
the third upper cheek tooth. Near the last tooth are the openings of the
four or five ducts from the orbital gland.
The =hard palate= is widest between the fourth pair of cheek teeth. It
has eight to ten curved ridges on either side of the raphé. Behind the
first pair of incisor teeth is the triangular incisive papilla, at which
the naso-palatine ducts open. The mucous membrane is usually pigmented.
The =soft palate= is thick except at its margins. In the resting state
of the parts it comes in contact with the oral surface of the
epiglottis. Between its anterior and posterior pillars on either side is
a marked tonsillar sinus, in which an elongated =tonsil= is situated;
this is reddish in color, about an inch long, and projects somewhat into
the fauces between two folds of mucous membrane.
The =tongue= is wide, thin, and very mobile. It is not pigmented, but
has a bright red color. The upper surface is marked by a median groove
(Sulcus medianus linguæ), and is thickly beset with short, pointed,
filiform papillæ, the free ends of which are directed backward. On the
root the papillæ are long and soft; similar papillæ occur on the lateral
walls of the isthmus faucium. The fungiform papillæ are small, and are
scattered over the dorsum and sides of the tongue, but are absent on the
root. There are usually two or three vallate papillæ on either side.
Small foliate papillæ are also present. In the inferior part of the tip
of the tongue is the =lyssa=, a fusiform cord, composed of fibrous
tissue, muscular tissue, and fat. In large dogs it is about two inches
(ca. 4 to 5 cm.) long.
[Illustration:
FIG. 327.—SKULL OF ADULT ST. BERNARD DOG, SCULPTURED TO SHOW THE
EMBEDDED PARTS OF THE TEETH.
_I1–3_, Incisors; _C_, canines; _P1–4_, premolars; _M1–3_, molars.
]