Agriculture Reference
In-Depth Information
forward projection of the mandible) are common in goats,
and they adversely affect feeding behavior (Smith and
Sherman, 1994). The teeth are held in the alveoli by dental
ligaments. In ruminants, the ligaments of the incisors are
loose, looking like old teeth, with a varying degree of
mobility.
The oropharynx is apparently a part of the oral cavity
proper, but they are separated by a symmetrical mucosal
fold, the palatoglossal fold (glossal = lingual), where the
entrance into the pharynx is considered. The oropharynx
continues to the epiglottis and is outlined by the tongue
ventrally, the soft palate dorsally, and the palatoglossal
folds laterally. The caudal border of the soft palate contin-
ues dorsally and laterally with two symmetrical mucosal
folds called palatopharyngeal folds, which outline the tran-
sition between the nasopharynx and the laryngopharynx.
Within the oropharynx, the ventral side of the soft palate
shows two slit-like openings, the entrances into the palatine
tonsils. The nasopharynx and the laryngopharynx were
described in The Respiratory System. This is the place to
consider the pharynx as a whole and to talk briefl y about
its conformation and functional anatomy. The soft palate is
a mobile structure, movable by contraction of three muscles:
one is the tensor, another one is the elevator, and the last
shortens the soft palate. All of them help during deglutition.
The muscles of the pharynx are constrictors and dilators.
The constrictor muscles are grouped in the fi rst, second,
and third constrictor muscles. There is also a muscle that
dilates the pharynx. The names of these muscles are related
to the bones or cartilages at their respective origin. Their
insertion is on the lateral and dorsal walls of the pharynx.
The deglutition is the physiological refl ex act following
the formation of the alimentary bolus. It starts with the
bolus pushing the soft palate dorsally, concomitant with
the contraction of the elevator of the soft palate, and of the
fi rst constrictor of the pharynx. At the same time, the soft
palate is shortened. The fi rst wave of contraction is fol-
lowed by the second and the third waves, under the action
of the second and the third constrictor muscles of the
pharynx. At the end of the deglutition, the pharynx dilates,
and the tensor of the soft palate restores the resting position
of the soft palate.
The mucosa of the vestibulum and of the oral cavity
proper attach to the teeth under the name of gingiva.
T
HE
S
ALIVARY
G
LANDS
The salivary glands, as annex structures of the oral cavity,
empty the saliva inside of the oral cavity. The role of saliva
is to mix with the forage during the mastication and to
contribute to the formation of the alimentary bolus. There
are two categories of salivary glands: scattered (minor) and
compact (major). The labial, buccal (under the cheeks'
mucosa), and lingual are the scattered salivary glands. The
compact, major salivary glands are the parotid, mandibu-
lar, and sublingual salivary glands.
The Parotid Gland
See Figure 6.19. Located between the base of the ear, the
Wing of Atlas, the caudal border of the mandible, and
the linguofacial vein, this is the largest salivary gland of
the goat. The parotid duct accompanies the facial vein
along the rostral border of the masseter muscle and opens
in the oral vestibulum opposite the fourth superior cheek
tooth (the fi rst superior molar).
The Mandibular Gland
This gland is partially covered by the parotid gland, the
external jugular vein, and its branches. Only the caudoven-
tral part of the gland is apparent. It is triangularly shaped,
and the mandibular duct travels rostrally to open under the
sublingual caruncle.
The Sublingual Salivary Glands
There are two sublingual salivary glands: monostomatic
and polystomatic. The monostomatic gland (with only one
excretory duct) is as long as the line between the fi rst and
the last lower cheek teeth and parallels the mandibular
duct. The major sublingual duct opens with the mandibular
duct under the protection of the sublingual caruncle. The
polystomatic gland (with many salivary ducts) is located
caudodorsal to the previous gland and has numerous short
excretory ducts that open into the lateral sublingual recess
(the narrow spaces under the tongue).
T
HE
E
SOPHAGUS
The caudodorsal opening of the laryngopharynx leads
into the esophagus. There are three segments of the esoph-
agus: the cervical part, the thoracic part, and a very short
abdominal part. In the cervical region, the esophagus lies
on the dorsal aspect of the trachea and is slightly oriented
to the left. In the thoracic cavity, it lies on the dorsal
aspect of the trachea, until the trachea bifurcates into the
two bronchi. In the rest of the thoracic cavity, the
esophagus runs between the aorta (dorsally) and the caudal
vena cava (ventrally). Passing through the esophageal
hiatus, the esophagus opens on the dorsal aspect of
the reticulum by an orifi ce called cardia. Cardia can be
T
HE
P
HARYNX
The second compartment of the prediaphragmatic diges-
tive system, the pharynx, consists of three parts: the oro-
pharynx, the nasopharynx, and the laryngopharynx.
