Biomedical Engineering Reference
In-Depth Information
a postorbital plate which separates the orbit from the
temporal fossa. Indeed, this is the case for all haplorhine
(anthropoids plus tarsiers) primates and one of the few
skeletal traits that distinguishes tarsiers from strepsirhine
prosimians. The size of both the eye and orbit varies among
species, but the relative size coincides with the behavioral
habits of the species (
Kirk, 2004
). In the owl monkey
(Aotus), a nocturnal species, the eyes and orbits are rela-
tively large compared to the size of the skull. In diurnal
species the orbits and eyes are relatively smaller.
Many morphological similarities exist between the eyes
of nonhuman primates and humans. The primate retina
contains both rods and cones for reception of visual stimuli.
All higher primates lack a tapetum lucidum. The central-
ized macula has an abundance of cones and visual acuity is
sharpest around the fovea centralis. Among monkeys and
apes the only known exceptions to this pattern of retinal
morphology are the nocturnal owl monkey (Aotus) with its
rod-enriched retina and fovea and the high density of cones
in the fovea of the trichromatic howler monkey (Alouatta)
(
Finlay et al., 2008
). The owl monkey is also the only
higher primate to lack a macula lutea.
As in humans, the lacrimal gland is located in the
superolateral portion of the orbit and the duct inferi-
omedially. The secretions of this gland constantly bathe the
cornea. Like humans, nonhuman primates develop age-
related pathologies of the eye such as cataracts, macular
degeneration, and loss of visual acuity.
The superior and inferior eyelids are single extensions
of the skin. In some species the superior lid may have
distinctive coloration. Raising or lowering the brows are
important components of the communicative behavioral
repertoire of primates. They can expose or conceal the
upper eyelids and widen or narrow the eye slit to display or
obscure the eyeball.
width and the ethmoturbinals are arranged more vertically
than horizontally. Bilaterally, the olfactory nerve (cranial
nerve I) has a limited distribution in the upper portion of the
nasal cavity and exits the region superiorly, passing through
the cribriform plate as numerous, small branches as in
humans (
Geist, 1933
). In higher primates, olfaction is not
highly developed compared to many other mammalian
groups. Despite this underdevelopment, some nonhuman
primates, particularly New World monkeys, exhibit scent-
marking behavior using either secretions from perineal or
sternal glands or urine (
Heymann, 2006
). Adult platyr-
rhines have apparently functional vomeronasal (Jacob-
son's) organs for chemical sensing whereas those of adult
catarrhines are only vestigial (
Martin, 1990; Dennis et al.,
2004; Evans, 2006
).
Lips
The mouth of all higher primates is characterized by
continuous upper and lower lips which in some species are
highly mobile and frequently used in social displays.
Consistent with this, the largest and best developed
mimetic musculature of higher primates, as in humans, is
that surrounding the oral commissure (Burrows et al.,
2006). Opening of the mouth to display the teeth is
common in some types of social encounters.
Dentition
Theupperdentalarchishousedinthealveolararchof
the premaxillae and maxillae. The lower dental arch is
housed in the alveolar arches of the two halves of the
mandible which in higher primates are always fused on
the midline. The shape of the dentalarchesrangesfrom
rectangular to semicircular or U-shaped depending on the
species and/or sex of the animal. Dentition is usually
described by quadrants of the mouth: right and left
maxillary (upper) and right and left mandibular (lower)
quadrants. Four classes of teeth (
Butler, 1978
) are evident
in each quadrant of higher primates (
Figure 4.6
). From
anterior (midline) to posterior these are incisor, canine,
premolar, and molar
Nose
The external morphology of the nasal region in higher
nonhuman primates is characterized by the lack of a rhi-
narium, lack of a primitive-type philtrum, and an upper lip
which is continuous across the midline inferior to the nasal
septum. The size and shape of the nasal bones and carti-
lagenous elements vary considerably between species and/
or sexes and contribute to facial prognathism. The two
basic patterns of primate nasal morphology divide along
evolutionary lines. The nostrils of most New World
monkeys are widely placed and outward facing, hence the
name platyrrhine. The nostrils of most Old World monkeys
and apes are closer together, forward facing, and are
separated by a narrow septum. Hence, these groups are
called catarrhines.
Concomitant with the closer approximation of the orbits
in all higher primates, the cribriform plate is narrower in
(
James, 1960; Marshall, 1933;
Swindler, 2002
).
The nomenclature used to describe teeth in higher
primates is not always consistent from one reference to
another (
Matshes et al., 2005; White and Folkens, 2005
).
The nomenclature used here is one of the most commonly
used for humans. It has also traditionally been used in
primate literature on dental morphology, development,
and evolution. It is based on quadrants and identifies each
tooth individually as to class (denoted by a single letter)
and order of its location for that class (denoted by
a number). Incisors are abbreviated I and are numbered
from the midline. I1 is the central incisor and I2 is the
