Biomedical Engineering Reference
In-Depth Information
and for the duration of life form a single unit in articulation
with the skull.
The seven cervical vertebrae of higher primates include
the commonly seen mammalian variations in the form of
the atlas, C1, and the axis, C2 (
Figure 4.10A
C
). The body
of a typical cervical vertebra is saddle-shaped, broad, and
relatively thin. The foramen in each laterally flaring
transverse process of cervical vertebrae C1 through C6
transmit the vertebral arteries between the thoracic inlet
and the cranium. The accompanying vertebral veins from
the dural sinuses in the cranial cavity pass through the
foramina transversaria of all seven certical vertebrae. In
higher primates the dorsal (posterior) arch of the atlas not
only lacks a spine but also is very narrow (
Figure 4.11
). The
spines of the axis and other cervical vertebrae are more
slender craniocaudally when compared to those of many
other mammals (see also the section “Skeleton” below).
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Brain and Pineal and Pituitary Glands
The primate brain is relatively large and incorporates more
complex structural modifications than the brain of most
other animals of similar body size (
Hines, 1933; Noback
and Montagra, 1970
). The major lobes of the cerebral
hemispheres (temporal, frontal, parietal, and occipital) are
all well developed. The frontal lobes overlay the reduced
olfactory bulbs and the occipital lobes overlay the cere-
bellum. Major sulci present in all higher primates are the
rhinal, Sylvian, and calcarine sulci. The sulcal pattern of
the cerebral cortex in higher primates varies from species to
species. The sulcal pattern of Callitrichidae is relatively
simple compared to the very complex patterns found in
Cebidae, Cercopithecidae, and Hominoidea.
Noback and
Moskowitz (1963)
described species variations in the brain
and spinal cord of higher primates and correlated these with
primary motor and sensory projection areas (see also
Martin and Bowden, 2000
). In all higher primates, the brain
receives blood from both the vertebral and internal carotid
arteries. The anterior and middle cerebral branches of the
internal carotid artery are usually the major source of blood
to the cerebral cortex.
The pituitary gland (hypophysis) is protected within the
sella turcica of the sphenoid bone, just caudal to the optic
chiasma. It is attached to the hypothalamus by a slender
stalk, the infundibulum, which pierces the thick dural roof
of the pituitary fossa known as the diaphragm sellae. In its
general organization, it closely resembles humans (
Miller
and Leonard, 1933
).
The pineal gland is anchored to the caudal dienceph-
alon, and is considered part of the epithalamus. In rhesus
macaques, it lies between the superior colliculi of the
tectum and extends caudally to the junction of the falx
cerebri and tentorium cerebelli, measuring approximately
2
FIGURE 4.9
New World monkey skull (Cebus apella, adult
female). (A) Superior-oblique view; (B) lateral view. Note the relative
width between the parietal eminences and zygomatic arches, lack of
development of supraorbital ridges, a nearly vertical facial profile asso-
ciated with little prognathism, and a wide ascending ramus of the
mandible. Sexual dimorphism of the skull is not marked among most New
World monkeys. (Drawings by Nancy Hong.)
monkeys differ in ear, nasal, and dental arch morphology as
well as in the degree of prognathism and sexual dimor-
phism. Palate length in most species is relatively short
when compared to skull length.
The position of the foramen magnum and the occipital
condyles that lie lateral to it varies from species to species,
but in all primates they are primarily ventral (inferior)
rather than dorsal (posterior). The flexure of the basicra-
nium associated with this positioning permits a more
vertical posture of
the trunk relative to the skull
(
Figure 4.8A
).
The temporomandibular joint lies immediately anterior
to the external acoustic meatus. The mandibular condyle is
well developed and broader mediolaterally than in ven-
trodorsal (anteroposterior) length. The angle of the
ascending ramus of the mandible varies among species and/
or sexes, but the temporomandibular joint is always posi-
tioned superior to the tooth rows. The coronoid process is
well developed since m. temporalis plays a major role in
primate mastication. The mandibular halves of higher
primates fuse at the midline early in postnatal development
3 mm in length and breadth (
Miller and Leonard, 1933
).
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