Page 387 - Anatomy and Physiology of Farm Animals, 8th Edition

372 / Anatomy and Physiology of Farm Animals

tongue, where the digestive tract continues (A)
as the pharynx.
VetBooks.ir comprises the hard palate rostrally and the
The dorsal wall of the oral cavity

soft palate caudally. The hard palate is
formed by horizontal elements of the
incisive, maxillary, and palatine bones, and
its thick mucous membrane covering is
characterized by prominent transverse folds
called palatine rugae. The soft palate is a
musculomucosal sheet that extends toward
the base of the epiglottis (see Chapter 19).
The equine soft palate is exceptionally long,
and the horse is uniquely unable to actively
lift the soft palate so as to permit passage of (B)
air from the oral cavity to the larynx. For this
reason, horses are obligate nose breathers,
unable to breathe through the mouth unless
the soft palate is abnormally displaced dor­
sad from its normal position ventral to the
epiglottis (Fig. 20‐2).

Teeth

Teeth are arranged in two dental arcades,
one associated with the mandible and one
with the incisive and maxillary bones.
Farm animals typically have a gap in each
arch between the front teeth (incisors) and Figure 20-2. (A) The equine soft palate nor­
the cheek teeth (see Fig. 4‐4); such a physi­ mally lies ventral to the margins of the epiglottis,
ologic gap is a diastema. The bit of the bri­ except during swallowing when it is briefly lifted
by the passage of the food/water being swallowed.
dle lies in the horse’s diastema. This position provides a broad, unobstructed pas­
Mammals typically exhibit heterodonty. sageway for air. (B) With “dorsal displacement of
That is, they have various types of teeth that the soft palate,” the soft palate is inappropriately
are specialized for different aspects of lifted to the dorsal side of the epiglottis. The long
prehension and mastication. All domestic palate hangs into the laryngeal vestibule and con­
animals also are diphyodont. This means stitutes a partial obstruction to air movement. In
they develop a set of deciduous teeth (also this position, the horse may breathe through his
called baby teeth or milk teeth) that fall out mouth, a pattern not normally possible.
and are replaced with permanent teeth. As
growing teeth emerge from the gums, they examination of the wear patterns of the
are said to erupt. When their occlusal occlusal surfaces.
(grinding) surfaces meet those of the teeth A tooth is anchored by its root in a
in the opposing arcade, they are said to have socket of bone called an alveolus.
come into wear. Eruption times of teeth are Connective tissue, the periodontium
consistent enough to permit accurate aging (also called periodontal membrane),
of young animals by observing their denti­ firmly attaches the root to the surround­
tion (see Tables 20‐1 and 20‐2). The age of ing bone in a specialized joint, the gom-
animals with a full set of permanent teeth phosis (see Chapter 6). The crown is the
can be only roughly estimated through part of the tooth visible above the mucous