Biomedical Engineering Reference
In-Depth Information
definitively descend into the scrotum. In species,
e.g. Erythrocebus patas, where the testes redescend late,
the scrotum does not usually become pendulous until
puberty. Prior to the redescent of the testes the scrotum is
represented by folds of loose skin adjacent to the midline.
Thus in these species the male perineum prior to puberty
resembles that of the female. Similarly the penis, although
pendulous at birth, may also retract prior to puberty, further
adding to the difficulty of sexing juveniles in some species.
Once puberty is passed both the scrotum and penis remain
pendulous.
Seasonal variations in the male perineum of species
with distinct breeding seasons include ascent of the testes to
positions closer to the external inguinal rings, partial
contraction of the scrotum, and diminished coloration of
the scrotum.
Prolapse of the bladder, vagina, uterus, and rectum are
all seen in nonhuman primates. Prolapses are much more
common in females than in males. The vagina, the uterus,
and/or the bladder can all prolapse through the vaginal
opening. These are all usually the result of weakness of the
ventral (anterior) vaginal wall. Prolapse of the rectum
occurs in both sexes due to weakening of the muscles of the
pelvic diaphragm or straining to defecate. Extreme
swelling of the sexual skin in females around the time of
ovulation can resemble the prolapse of hollow viscera.
the great and lesser apes as well as monkeys. Some New
World monkeys have prehensile tails whereas no Old World
primates have true prehensile tails.
The second major morphological grouping of primates
occurs within the Old World primates. Nonhuman Old
World higher primates are subdivided into apes and
monkeys. This division is based on a number of criteria but
the most obvious are the differences between primarily
quadrupedal locomotors (Old World monkeys) and more
mixed forms of locomotion (apes). The latter group is
characterized by lengthening of the forelimbs and further
ventral
dorsal flattening of
the thorax among other
e
criteria.
These first two morphological groupings follow evolu-
tionary lines. The next morphological grouping, however,
cuts across evolutionary boundaries and is based on habitat
use. The criterion here is whether the species is primarily
terrestrial or arboreal. Terrestrial monkeys tend to have
relatively greater sexual dimorphism, larger body sizes,
longer limbs, and shorter digits than their arboreal coun-
terparts. Elongated limbs, particularly forelimbs, however,
are characteristic of arboreal monkeys making extensive
use of suspensory locomotion. In morphology related
directly to habitat use, arboreal monkeys in the Old and
New World may more closely resemble each other than
either resemble Old World monkeys with highly terrestrial
habits.
Like habitat, grouping primates by dietary preference
also cuts across evolutionary boundaries and includes
species throughout the world. Dietary preferences are
broadly grouped as omnivorous (insectivorous), foliverous,
or frugivorous, and are mirrored in gastrointestinal modi-
fications from dentition to gut. Folivores in particular have
evolved gastrointestinal modifications which help maxi-
mize energy and storage from food with high cellulous
content. Frugivores frequently have larger home ranges
which are adaptive for survival in both abundant and lean
seasons.
Another criterion for categorizing nonhuman primate
morphology is sexual dimorphism. In some species there is
little overall morphological difference between the sexes
whereas in others there is a tremendous difference both in
size and shape. Sexual differences tend to be greater in
terrestrial than in arboreal monkeys. In species where there
is sexual dimorphism it is usually evident in body size, hair
coloration, and tooth size, particularly the length of the
upper canine.
Age also plays a key role in nonhuman primate
morphology. At birth the neonate is well developed, alert,
and capable of clinging to its mother's or father's body hair.
These roles are reflected in the relatively large size of head,
hands, and feet at birth. During growth the center of mass of
the body moves caudally and the center of mass of the
limbs moves proximally. The juvenile morphology includes
CONCLUSIONS
The morphology of all primates follows a pattern which is
generally that of an unspecialized mammal including five
well-developed digits on each of the four extremities. The
considerable variability of this pattern within the order can
be grouped according to various evolutionary and/or
functional criteria. The evolutionary divergence between
the two primate suborders is reflected in morphological
differences between prosimians and the more numerous
and diverse anthropoids or higher primates with more
extensive ranges in both the Old and New Worlds. Readers
are again advised that an alternate, and increasingly more
popular, division of primates into strepsirrhines and hap-
lorrhines groups tarsiers with anthropoid primates rather
than prosimians. Although we have chosen to follow the
more traditional division of the primate order, and thus not
include a consideration of tarsier functional morphology in
this chapter, readers should be aware that members of that
taxon indeed share many elements of their morphology
with anthropoid higher primates.
The first major morphological grouping of higher
primates is by geographical location, i.e. Old or New
World. New World monkeys have three premolar teeth in
each quadrant whereas all Old World higher primates have
only two. All New World primates are monkeys and all are
arboreal. Old World higher primates include humans and
Search WWH ::




Custom Search