Functional Morphology - Nonhuman Primates in Biomedical Research - page 97

two premolars, i.e. P3 and P4. This distinction between the
two evolutionary groups is evident in both the deciduous
and permanent dentition ( Swindler, 2002 ).
The last teeth in the permanent, or adult, dental arch are
the three molars: M1, M2, and M3. Reduction or even
absence of the third molar is more common in, but not
limited to, New World monkeys. The Callitrichidae (with
the exception of Callimico) are the only higher primates
that consistently have only two molars per quadrant. As in
premolars, upper molars generally have three roots whereas
lower molars generally have only two. All molars typically
have four to five cusps although the number may be
reduced or expanded, especially in the last tooth of the row.
Expansion of the third molar is most common in the longer
faced species of Old World monkeys. There is, however,
considerable variability even between closely related
species. In Old World monkeys, the molar crowns display
strong transverse ridges between pairs of cusps and
constriction between mesial and distal pairs of cusps
resulting in the closely approximated cusps forming two
distinct ridges which are oriented lingual

into a nasopharynx located caudal to the nasal cavities,
an oropharynx situated caudal to the oral cavity, and
a laryngopharynx caudal to the larynx. The structures
comprising each of these pharyngeal regions, including
nerve and blood supply, follow the pattern described for
humans. A major difference between the human and
nonhuman primate pharynx, however, lies in the latter's
relatively narrower width and its angulation from head to
neck. In large part, the angulation mirrors that of the
cranial base which forms an obtuse angle in nonhuman
primates similar to that of other mammals, with the result
that the pathway from the nasal and oral cavities to the
pharynx is close to a straight line, rather than angled at
approximately 90 as in humans ( Figure 4.8A ). In addi-
tion, the superior constrictor is more extensively attached
to the cranial base in nonhuman primates ( Aiello and
Dean, 1990 ). (See the section “Respiratory system” below
for the larynx.)
Three pairs of salivary glands provide secretions to the
mouth. Each parotid gland is ventral (anterior and inferior)
to the external auditory meatus. The caudal portion of the
gland lies superficial to the internal carotid artery, the
internal jugular vein, and numerous nerves. It is traversed
by the motor trunk of facial nerve (cranial nerve VII) to the
mimetic musculature, the external carotid artery, the
external jugular vein, and other smaller nerves and vessels.
The parotid duct enters the oral cavity lateral to the M 2 . The
submandibular (submaxillary) gland lies inferior and
medial to the angle of the mandible in close proximity to
the hypoglossal nerve (cranial nerve XII) and the major
vessels in the neck. The submandibular duct passes deep to
the sublingual gland and the lingual nerve prior to entering
the floor of the mouth ventral (inferior) to the tongue. The
sublingual gland, the smallest of the three salivary glands,
lies immediately deep to the oral mucosa along the medial
side of the mandibular body cranially (anteriorly). It lacks
a single duct and instead has numerous openings directly
into the floor of the mouth.
Among Old World monkeys, the mouths of the Cerco-
pithecinae but none of the Colobinae have additional
unique characteristics in that they have cheek (buccal)
pouches opening into the floor of the oral vestibule opposite
the lower premolars. These superficial pouches extend for
a considerable distance into the neck on either side of the
midline. Each pouch is covered by muscle fibers derived
from the m. buccinator which have herniated through the
overlying m. platysma. The mucous membrane lining the
pouch is continuous with that of the rest of the buccal
vestibule of the oral cavity including glandular tissue
producing the digestive enzyme amylase ( Rahaman et al.,
1975 ). Cheek pouches are frequently used to store food
which will later be pushed back into the oral cavity
(sometimes with the assistance of hands placed external to
the pouch) for further mastication prior to swallowing. The

buccally. The
resultant molar is called bilophodont (see Swindler, 2002 ,
for details on the dentition of each individual species).
The innervation and vascular supply to the teeth as well
as the morphology of the supporting gingival and peri-
odontal structures are similar in all primates, including
humans. As in humans, periodontal health decreases with
age and diet is considered to contribute to intergroup
differences within a single species ( Phillips-Conroy et al.,
1993 ).

e

Oral Cavity
Palate length in most species is relatively short when
compared to skull length. Within the oral cavity the tongue
plays an important role in maintaining food between the
grinding surfaces of the teeth. The tongue of nonhuman
primates is relatively short and flat and is not as rounded as
in humans ( Figure 4.8A ). It also lacks the food-acquiring
mobility of some other mammals. The tongue surface of
primates, including humans, has an abundance of papillae
with numerous taste buds and their associated sensory
nerve endings. The tongue is divided into an anterior two-
thirds and a posterior one-third by a V-shaped row of
circumvallate papilla. The anterior two-thirds of the tongue
has numerous fungiform papillae particularly near the tip.
Smaller filiform papillae give the entire tongue a relatively
smooth appearance. On the posterior one-third of the
tongue foliate papillae lie adjacent to the lingual tonsils.
The line of the passage from the oral cavity through the
oropharynx and into the laryngopharynx is nearly straight
( Geist, 1933 )( Figure 4.8A ).
The general organization of the nonhuman primate
pharynx is very similar to that of humans and is divided