Humans are contrasted with chimpanzees
to illustrate the unique features of our anatomy. Other primate
species are included when they are needed to demonstrate a point.
Primates have four types of teeth - incisors, canines, premolars and molars. Incisors are like tiny shovels or spatulas that cut food. Canines are generally pointed, stabbing teeth that can serve as weapons in most primates. Premolars and molars have large crown surfaces that shear and crush food during mastication.
The number and type of teeth are
summarized by listing only elements on one side from incisor,
canine, premolar to molar (mesial to distal) for each jaw. Thus
the primitive mammalian formula of 18.104.22.168./22.214.171.124. represents
a hypothetical mammalian ancestor with 44 teeth. Whatever the
ancestral condition, no living primate has more than three incisors
or three premolars on each side in either maxilla or mandible.
Prosimians and Platyrrhines have three premolars; Catarrhines
have only two. Third molars are often absent in some primate
genera. Once a tooth is lost in a species, it is usually not
reproduced again. Thus ancestral forms generally may have more
teeth, but not fewer teeth of a particular kind than their descendants.
A tooth consists of a crown, the
portion covered with enamel, and a root of dentine covered with
cementum. The interior of the tooth is the pulp chamber that
contains soft cellular tissue. The primary mineral in both bone
and dental structures is crystals of apatite - a form of calcium
phosphate. Dentine is a bone-like substance (about 75% mineral)
but enamel is much more heavily mineralized (96% mineral by weight).
Cementum, whose composition differs only slightly from that of
dentine, attaches the tooth to its periodontal ligament and provides
a dynamic interface between tooth and surrounding bone, while
enamel forms a crystalline cap over the working surface of the
Primates have two sets of teeth during their lives, a deciduous set that is replaced by permanent teeth during childhood and adolescence. The human dental formulas are:
Note that humans have no deciduous
molars. Substantial individual variation occurs in tooth number,
but most often the variant is the loss of a tooth at the boundary
between tooth kind (incisor/canine/premolar/molar). Infrequently
there can be supernumerary teeth or additional teeth near a boundary.
In traditional notation the most mesial permanent premolars and
the most distal incisors are lost in primates. Consequently the
premolars of primates are designated the second, third, and fourth
premolars -- presumably homologous to the primitive mammalian
second, third, and fourth premolars. Humans are also missing
fourth premolars, leaving us with premolars three and four. For
example, the notation pm3 refers to mandibular third premolar,
the premolar next to the canine on the lower jaw.
The greatest differences between
humans and chimpanzees occur in the canine teeth. Small peg-like
human canines do not project from the tooth row. In contrast,
chimpanzee canines are much larger, robust, and project far above
their tooth row. Diastemas, gaps in the tooth row of the maxilla
allow projecting mandibular canines to pass the opposing canine
and incisor during occlusion. The maxillary canine passes the
buccal side of its opposing pm3, allowing the lingual surface
of the canine to make contact with a blade-like sectorial
surface on the premolar. Humans lack the large diastema and the
human pm3 is non-sectorial. Human anterior teeth (canines and
incisors) are greatly reduced in size and human incisors are
positioned close to a transverse plane that passes through the
canine teeth. Chimpanzee incisors are positioned well forward
of this plane. Consequently the parabolic or elliptical human
dental arcade contrasts sharply with the U-shaped arcade of chimpanzees.
Human molars tend to be rounder and more compact than chimpanzee
molars. Occlusal molar surfaces of human teeth are relatively
flat, and quickly become even flatter with attrition (return to outline).
The following figure illustrates the terms used in orienting and describing the body.
is the position is a ventral view of the a body lying on its
back or standing with arms at the side with face, palms and toes
The skull consists of 28 bones that
are conveniently described as the bones of the calvarium (supporting
and surrounding the brain) and those of the face. Tiny bones
of the middle ear, the conchae and vomer in the nose, and the
ethmoid of the orbital vault are not easily seen. Although usually
not considered part of the face, the hyoid bones form a skeletal
element for the larynx. In addition to the openings that represent
the eyes, nose, mouth and ears, the skull has numerous foramina
for the passage of nerves and vessels. The bones of the cranium
(the skull minus the mandible) are joined by irregular sutures
that are obliterated after growth ceases.
Seven major differences between
humans and chimpanzee skulls include:
(1) brain volume -- The human skull
has a three -fold greater endocranial volume -
reflecting a larger brain size, about 1200 cc in human and about
400 cc in chimpanzees. The larger size of the human calvarium
allows ample surface area for the attachment of the powerful
M. temporalis. Fibers from this muscle attach to the skull in
the fossa temporalis and pass behind the zygomatic arch
to insert on the coronoid process and anterior margin
of the ascending ramus of the mandible. The temporal lines
or temporal crests on the calvarium mark the terminal
fibers of M. temporalis. If brain volume is small, producing
a small calvarium (as in a chimpanzee), there may not
be enough surface area on the calvarium for M. temporalis fibers
to attach. Where fibers from the opposite muscle meet, a bony
crest, in this case a sagittal crest is formed. Crest formation
usually signifies a small calvarium relative to muscle size.
|Species||Lower 95% Limits for Mean||Upper 95% Limits for Mean||
The larger human brain volume also means that the calvarium is large relative to the size of the face. As the brain expands (comparing chimp and human), it appear to flex on an axis around the pituitary fossa. This produces flexion of the cranial base, a downwards shift in the posterior part of the cranium, and a forward rotation of the foramen magnum.
Expansion of the occipital lobes and cerebellum balloons the posterior cranial fossa, that in turn correlates typically with an asymmetrical cranial venous sinus system. In the human, a superior sagittal sinus drains venous blood in a transverse sigmoid route to the internal jugular veins. Enlarged occipitomarginal sinus systems typical of humans are infrequent in chimpanzees. The human middle cranial fossa expands with enlarged temporal lobes of the brain expanding the mid-section of the calvarium outward above the petrous portion of the temporal bone and the glenoid fossa. In chimpanzees, the calvarium is narrower than the cranial base but the human calvaria has its maximum width high on the parietal eminences rather than low at the cranial base. The anterior cranial fossa expands with the human frontal lobes. Consequently humans lack the postorbital constriction that occurs in chimpanzees and humans exhibit frontal eminence (forehead) above a greatly less obvious supraorbital torus (eyebrow ridge). Olfactory nerve tracts pass through the cribriform plate, a sieve-like structure in the middle of the ethmoid bone. In humans the median plane of the cribriform plate is the site of a process, the crista galli. This process is diminutive or absent in chimpanzees.
Ballooning of the calvaria in the temporal and occipital areas associated with the expansion of brain volume produces an apparent forward shift in the relative position of the foramen magnum. The human foramen magnum lies on a line, the bitympanic line, that connects the most inferior points on the lateral end of the right and left tympanic plates. The chimpanzee foramen magnum lies well behind the bitympanic line.
(2) nuchal crests -- Muscles that attach to the cranial base serve to position, move, and stabilize the head and cervical vertebrae. From a functional perspective, the skull is also the most superior point of origin for muscles (such as M. trapezius) that provide movement and stability to the back and shoulder. Consequently, some of the powerful muscles that attach to the skull have large attachment surfaces. The human occipital is a cup-like bone with a noticeable eminence, the external occipital protuberance. It is marked by nuchal lines and markings that represent attachment surfaces. The nuchal crests of the chimpanzee are more extreme. Its small skull combined with a much more robust musculature produces strong crests. Due to the flexion of the cranial base with expanded endocranial volume, the superior nuchal line is lower on the human skull.
(3) mastoid process -- The human mastoid process, the attachment surface of the sternocleidomastoid muscles, is distinct and separated from the outline of the occiput by a digastric fossa.
(4) premaxilla -- The smaller human incisivum, a homologue of the chimpanzee premaxilla, unites with the maxilla near the time of birth. The chimpanzee premaxilla is expanded to support the large and forward projecting incisors. It unites with the maxilla postnatally and the suture between it and the maxilla becomes obliterated.
(5) facial prognathism -- The projection of the face beyond the calvaria is greater in chimpanzees than humans. Flat faces are called orthognathic and projecting faces are called prognathic. The craniofacial angle, the angle between the most anterior point on the maxilla, the most anterior point of the sphenoid bone and the most anterior point of the foramen magnum, is used to quantify the extent to which the face projects beyond the neurocranium. Since this angle can not readily be measured on intact skulls, the angle that a sellion-prosthion line makes with the Frankfort plane serves as a convenient measure of facial projection. [The "Frankfurt plane" is the plane that passes through porion (right and left) and orbitale (right and left).] The porion is the most lateral and superior point of the external auditory meatus. The orbitale is the lowest point on the infraorbital margin. The sellion is the deepest point in the hollow beneath the glabella in the median plane. The glabella is the most anterior point in the median plane on the supraorbital torus. The prosthion is the most anterior point on the maxilla in the median plane.]
(6) chin -- The human mandible is reinforced by a bar of bone, the mental protuberance, that strengthens the symphysis, the union of right and left halves of the bone. The lingual or posterior surface of the symphysis bears a pair of genial tubercles that represent muscle attachment sites for M. genioglossus and M. geniohyoid. The ape mandible lacks a mental protuberance and is reinforced by an inferior transverse torus or "simian shelf". Viewed from above, the contrasting shape of the dental arcades is distinct.
(7) hyoid -- The human hyoid is a U-shaped bone just above the larynx. The stylohyoid ligament attaches the lesser horn of the hyoid to the styloid process of the temporal bone. Generally, these styloid processes point to the lesser horns of the hyoid bone. The chimpanzee hyoid is expanded anteriorly to accommodate a laryngeal air sack, and is located higher in the neck (return to outline).
The human vertebral column consists of 33 vertebrae divided into five functional regions.
1. Seven cervical vertebrae, easily recognized by their transverse foramina, form the skeleton of our neck. The joints (articular surfaces) between cervical vertebrae are very mobile.
2. Twelve thoracic vertebrae, mobile only in the coronal plane, support the ribs.
3. Five robust lumbar vertebrae in the lower back are tightly articulated to withstand the weight of the torso.
4. Five sacral vertebrae fuse to form the sacrum, the component of the axial skeleton in the pelvis.
5. Four caudal vertebrae extend downward from the sacrum. In adults these caudal vertebrae unit to form the coccyx, a hidden human tail that partially blocks the inferior pelvic aperture.
Viewed from the side, humans have a series of four curvatures. The dorsal outline of the cervical and lumbar regions are concave while the thoracic and sacral regions are convex. The forward curve of the lumbar region is called lordosis and that of the thoracic region is called kyphosis.
Chimpanzees generally to have one more thoracic, one less lumbar vertebra, and one less caudal vertebra than do humans. Both normally have seven cervical vertebrae and normally the combined thoracic, lumbar, and sacral regions consists of 22 vertebrae. Chimpanzees lack the extreme curves of the human column, and the angle between the lumbar and sacral region is more acute .
(return to outline)
The human chest consists of 12 paired
ribs that articulate with the vertebral column. Ribs I through
VII attach ventrally to the sternum. Ribs VIII through X terminate
in cartilage extensions that eventually fasten to the sternum.
Ribs XI and XII have free distal ends. The sternum is composed
of six flat bones that fuse in adults to three units, the manubrium
(segment I), body (segments II through V), and xiphoid process
(segment VI). In some persons, especially in old age, the three
units of the sternum may fuse to each other.
Consistent with their extra thoracic
vertebra, chimpanzees usually have one extra rib (13 pairs). The
human rib cage is slightly broader for its depth than the chimpanzee
and the human thorax is less funnel-shaped. Chimpanzee ribs are
also somewhat rounder in cross-section than human ribs (return to outline).
The shoulder is formed by the humerus, clavicle and scapula. The clavicle attaches firmly to the manubrium and acts as a strut to hold the shoulder joint away from the chest. Distally, the clavicle articulates with the acromion process of the scapula, a large triangular flat bone in the back of the shoulder. The glenoid cavity of the scapula articulates with the head of the humerus.
The most striking difference between
the chimpanzee and human shoulder is in the proportions of the
scapula. Human arm strength, much less powerful in movements when
in a raised position, is reflected in the shape of the scapula
that provides attachment surfaces and lever arms
for muscles (return to outline).
The upper arm is a single bone, the
humerus. The forearm is formed medially by the ulna, which articulates
firmly by a hinge joint to the humerus, and laterally by the radius
which is firmly attached to the hand. The radius pivots on the
humerus and ulna to supply hand rotation (pronation) and is attached
to the ulna by powerful interossesous muscles and ligaments.
The head of the humerus is useful
in identification of gender of a mature unknown cadaver. If the
maximum diameter of the head is greater than 45 mm, the individual
is probably male. If the head diameter is less that 42 mm, it
is probably female.
The chimpanzee distal humerus contrasts
with the human. The human lacks the robust lateral supracondylar
ridge, a high and robust lateral epicondyle, and the steep, sharp,
lateral margin of the olecranon fossa . The chimpanzee forearm
is relatively long in comparison to humans . Chimp radius and
ulna are more curved than in humans and the chimpanzee distal
radius has a radiocarpal joint surface that diverges medially.
The major differences between human and chimpanzee limbs are contrasts
in relative proportion. Chimpanzees have large powerful arms,
slightly longer than their very short legs. Human arms are about
70% as long as human legs.
|Species||Intermembral Index||Humerofemoral Index||Brachial Index||Crural Index|
|Pygmy chimpanzee (male & female)||102.2||98.0||91.9||82.6|
The hand has three skeletal regions:
(1) The carpus, a series of eight carpals, form the wrist. (2)
The hand consists of five metacarpal bones. (3) Phalanges form
the skeleton of the fingers. The thumb, digit I has two phalanges
(proximal & distal), while digits II through V have three
phalanges (proximal, middle and distal).
The chimpanzee hand is notably different
from the human hand in the relative length of its digits. The
chimp thumb is much shorter than in humans, phalanges exhibit
much more robust insertion areas for flexor tendons, and metacarpals
have transverse ridges across their heads that limit dorsiflexion
(return to outline).
The pelvic girdle is formed by the
sacrum, coccyx, and the two coxae. Each coxa is attached by strong
ligaments to the sacrum and to each other at the pubic symphysis.
A coxa is formed by the fusion of three bones, the ilium, ischium,
and pubis, which meet in the acetabulum or hip socket.
The human female has a larger birth
canal than does a male. Consequently there is a constellation
of characters that can be used to identify the gender of an unknown
pelvis. The pelvic inlet of females is larger and has a greater
absolute circumference. The superior ramus of the pubic bone is
longer, increasing the pubic/ischium ratio. The greater sciatic
notch is wider and forms a longer angle. The increased pubic length
and laterally displaced ischia result in a wider subpubic angle.
The growth and remodeling of the pubis produces extra bone at
the symphysis, leaving a concave inferior ramus, a ventral arc
that represents a previous border of the symphysis, and a narrow
inferior pubic ramus. The female pubic symphysis is likely to
be longer in its superior-inferior diameter and smaller in its
dorsal-ventral diameters than is that of a male. Females are more
likely to have a well-developed preauricular sulcus, and those
who have borne children may have pits or guttering along the dorsal
border of the pubic symphysis. Since they have smaller femurs,
females have smaller acetabula.
Differences in the pelvis reflect
the differences between the habitual bipedal locomotion of humans
and quadrupedal movements of chimps . The pelvis of the two primates
have radically different form and locomotor function. The relative
width of the iliac blade (width/length x 100) is much larger in
humans (125.5) than in chimpanzees (66.0). The human ilium is
broad and low, while the chimp ilium is narrow and high. The human
has a barely noticeable iliac pillar or thickening which extends
from the iliac tubercle to the acetabulum. The human has an anterior
inferior iliac spine. The human acetabulum is larger, reflecting
the larger head of the femur, and the superior border of the acetabulum
is reinforced to sustain the pressure of bipedal walking. The
inferior border of the ilium near the auricular surface forms
a greater sciatic notch in humans. The auricular surface is larger
in the human. The ape sacrum is long and narrow (return
The femur, the bone in the thigh, articulates ball and socket fashion in the acetabulum of the coxa. The lower leg contains a large medial bone, the tibia, which articulates with the femoral condyles to form the knee. Lateral to the tibia, the fibula is a small, irregular bone that provides attachment surfaces for muscles. Projections on the distal ends of tibia and fibula, the medial and lateral malleolus, form a secure slotted proximal structure for the ankle joint.
As in the head of the humerus, a maximum diameter of 45mm or greater for the femur head indicates a male gender.
The human femur is longer than the
chimp femur and usually has an elevated pilaster that supports
the linea aspera down the shaft. The angles of the head, shaft,
and condyles contrast markedly with those of the ape. The load
axis never intersects the shaft in a chimpanzee femur. The femoral
condyles of the human are larger and more elliptical than are
those of the chimp. The human femur has a larger articular surface
and mid-shaft circumference when compared to the arm than does
the chimpanzee. The chimpanzee has a similar ratio between femur
length and tibia length but the chimpanzee leg (including both
femur and tibia length) is much shorter relative to the arm. The
chimpanzee proximal tibia is smaller, less well supported by the
shaft, and has condyles than are more convex than is usual in
humans(return to outline).
Like the hand, the foot has three
anatomical regions: (1) The seven bones of the tarsus form the
ankle and proximal half of the foot. (2) The middle portion of
the foot consists of five metatarsals. (3) Phalanges, the skeletal
elements of the toes, have the same number and arrangement as
in the fingers.
The primary difference between the
human and chimp foot is the contrast between prehensile functions
of the ape foot and the anatomy of bipedal striding in the human.
The chimpanzee foot has an opposable hallux and long phalanges.
The human foot has greatly reduced digits, with all metatarsals
parallel and an increase in the lever arm of the tarsus for striding.
In the human foot, a longitudinal arch provides a shock absorbing
and weight distribution system. The orientation of the ankle joint
allows the tibia to take a straighter path over the foot during
walking (return to outline).
The bones of the limbs and vertebral
column are endochondral, that is, they are first formed
as cartilage that is gradually replaced with bone. Centers of
ossification in the cartilage gradually enlarge to form the bone.
The body or shaft in long bones is called the diaphysis,
or primary center of ossification. The ends of long bones have
secondary centers of ossification, called epiphyses, that
are separated from the diaphysis by cartilage plates. Eventually,
the cartilage plates, the epiphyseal cartilage, are replaced by
bone and the epiphyses unite with the diaphysis to form a single
bone. The flat bones of the skull, mandible, and clavicles are
intramembranous bones, formed from membranes, and generally do
not have epiphyses (return to outline).
Much of primate anatomy reflects
habits of movement and commonly utilized substrate. Since the
powerful legs of most primates are slightly longer than their
arms, the pelvis is normally higher than the head when standing
quadrupedally. However a few species exhibit extreme locomotor
specialization, emphasizing arms for arm-swinging, legs for leaping,
or arms and legs comparable in length for quadrupedal climbing
or walking on the ground. Thus, limb length (Intermembral Index
or IM = Length of Humerus + Radius x 100/ Length of Femur + Tibia)
can serve as an index of the relative emphasis upon the arm versus
the leg for propulsion:
1. Short limbs with leg and arm comparable - quadrupedal and arboreal
These animals walk on larger horizontal
tree branches as if they were pathways. Short, usually robust,
arms and legs lower their center of gravity. IM index is usually
about 80 but approaches 100 in howler monkeys. Other characteristics
include moderately sized fingers and toes; very prehensile hands
and feet; and relatively mobile shoulder joints located and directed
sternally on the thorax. Some species, especially those which
perform spectacular leaping feats, have flexible, elongated backs
(with extra vertebra) and powerful musculature associated with
the back and hind limb. A few species in the Americas have somewhat
prehensile tails that serve to anchor the animal when it feeds
near the ends of branches.
2. Long limbs with leg and arm of
equal length - quadrupedal and terrestrial
Terrestrial quadrupeds tend to have
shortened digits and elongated, robust tarsal and metatarsal elements.
IM index is above 90. The shoulder joint, lying alongside the
narrow and laterally flattened thorax, is oriented toward the
ground. The weak clavicular-sternal joint is easily dislocated
from the segmented sternum. Arms and legs, modified for powerful
sagittal motions, have a relatively small range of movement. The
humerus bears a prominent deltoid process (the attachment surface
for the M. deltoideus) and the ulna has a large olecranon process,
the insertion point of the M. triceps brachii, a powerful forearm
extensor. Hands are pronated when in contact with the ground.
One species, the patas monkey, is digitigrade (like a cat), with
specialized anatomy for terrestrial running in which only fingers
and toes make contact with the ground.
3. Very long limbs with leg and arm of comparable length - quadrupedal and arboreal with an emphasis on quadrupedal climbing and suspension
A few primate species in the Family
Lorisidae combine quadrupedal suspensory climbing with quadrupedal
arborealism, requiring great joint mobility and wide range of
movement. IM index is about 90. Their hands and feet are particularly
4. Arm longer than leg - brachiation
Brachiation (arm swinging) is a special form of locomotion
in which the body is suspended below branches. It allows utilization
of small branches near the fringe of a tree canopy since the brachiator
is suspended beneath its handholds. In contrast, a large bodied
quadruped that tries to walk on a small branch has difficulty
balancing as the supporting tree limb bends. A brachiator can
easily exploit the very fringe of a tree canopy by dispersing
its weight to the ends of several branches. New World brachiators
use their prehensile tail as a fifth prehensile limb to further
disperse weight. Most rapid brachiation is attained by using gravity
to convert vertical height to speed. IM index is 100 or above.
Brachiation generally is associated
with major alterations in the arm, hand, and thorax. The shoulder
joint is positioned laterally and cranially on a barrel-shaped
thorax. Robust muscles attach to the sternum, vertebral column,
head, and rib cage, stabilizing the shoulder. The more powerful
the arm movements, the more robust the stabilizing musculature
must be. The clavicle acts a strut to stabilize the shoulder joint
against a sternum whose segments unite to form a single bone.
This clavicular-sternal joint is very strong and is not easily
dislocated. A relatively round head of the humerus reflects a
very wide range of motion. Additional elbow strength results from
a more distinct separation of the radius and ulna on the articular
surfaces of the distal humerus. The olecranon process of the ulna
is small, allowing full extension of robust forearms. Brachiators
tend to have reduced thumbs. If a thumb is present, it is folded
out of the way against the palm where it does not interfere with
elongated fingers that hook or snag handholds. The lumbar region
of the vertebral column is shortened and stabilized, and a very
mobile hip joint allows the foot to grasp anchorage in a wide
range of positions.
There are several types of brachiators.
Gibbons and siamangs, who use arm swinging as a major means of
travel, are the best brachiators. Chimpanzee, gorillas, and humans
are capable of this type of brachiation, but do not practice it
as a primary means of locomotion. The orangutan combines quadrupedal
climbing and brachiation, but like chimpanzees and gorillas, is
typically a terrestrial quadruped.
At least one New World primate, the
spider monkey, practices a variation of brachiation in which the
body is kept vertical while brachiation is performed by hands,
feet and sometimes the tail. This requires unusually long legs
and mobile hips. When moving at slower speeds or while feeding,
the spider monkey behaves as an arboreal quadruped. Its tail is
the most prehensile of any primate.
5. Arm longer than leg - quadrupedal knuckle-walking and fist walking
Knuckle-walking is quadrupedal locomotion
with the hands pronated and fingers flexed resulting in dorsal
surfaces of the middle phalanges contacting the ground, supporting
the weight on the knuckles. Gorillas and chimpanzees are habitual
knuckle-walkers, whereas orangutans usually move quadrupedally
with the hand made into a fist. IM indexes for the chimpanzee,
gorilla, and orangutan are 102, 116, and 139, respectively.
6. Leg longer than arm - leaping
A special class of leaping locomotor
behavior, in which the body is positioned vertically at rest,
is called vertical clinging and leaping. It requires powerful
hind limbs to propel the leap as well as to break the impact of
landing. Most (but not all) vertical clinging and leaping species
have a tail that is used maintain attitude control during leaps.
Rapid movements are so well-coordinated during flight that the
animal transits the crown of a tree without appearing to make
contact with branches. This visual impression of suspending the
laws of gravity fueled many "ghost" myths associated
with vertical clinging and leaping primates. There is a tendency
toward elongation of tarsal elements, especially calcaneus and
navicular. Posterior elongation of tuberosity of the calcaneus
serves as a robust lever arm for M. gastrocnemius and M. soleus,
powerful flexors of the foot. The tendency for fusion of the tibia
and fibula is fully expressed only in the tarsier. IM index is
7. Leg longer than arm - bipedalism
Though obligate bipedalism
is found only among humans, many other primate species are capable
of facultative bipedalism. Foot specializations for bipedalism
include an enlarged and robust tarsal region, greatly reduced
phalanges, and strong ligaments that bind tarsals and metatarsals
into shock-absorbing longitudinal and transverse plantar arches.
A large calcaneus tuberosity acts as a lever arm for plantar flexion.
The most unique character of the long, robust legs is the placement
of the knees (when in anatomical position) close to the median
sagittal plane, functionally beneath the body's center of gravity.
The knee itself is adapted to locking in full extension with deep
groves to stabilize the patella, a bone that forms in tendons
of the quadriceps muscle. The broadened hip becomes a primary
weight-bearing joint, characterized by an enlarged femur head
as a weight-bearing surface. Pelvic anatomy is dramatically rearranged.
A relatively broad sacrum positioned above the hip joint transfers
weight to femur head via a wide and robust illium. A shortened
ischium places the ischial tuberosity relatively close to the
acetabulum. The vertebrae, increasing in size progressively from
skull to sacrum, are arranged in a ventral-dorsal S-shaped curve
above the pelvis. Though free of locomotor tasks, the arm retains
the range of movement seen in brachiators. IM index is 70.
8. Climbing by nails
Elongated and laterally compressed
nails of callithricines have the functional attributes of claws.
Although they climb by grasping small branches, they are able
to use these specialized nails to cling to relatively flat, vertical
surfaces of larger trees. IM index ranges from 70 to 80 (return to outline).
Color vision is a primate characteristic
that presumably reflects our arboreal ancestry. There two types
of photoreceptors in the primate retina: rods which function better
at low light levels (scotopic vision), and cones which respond
to much higher light intensities (photopic vision). The eyes of
most diurnal mammals have cones more numerous toward the
center of the retina (the region of sharp focus) and more rods
toward the periphery. Nocturnal primates have only rod
photoreceptors in the retina. The retina of higher primates has
a macula lutea (yellow spot) of cones. The fovea, a small depression
in the center of the macula in which there is only a single layer
of cones, is the area of keenest vision and the target of focusing
by the lens.
Color vision is produced by photosensitive
pigments that differentially absorb wavelengths. Color perception
depends upon the relative degree to which each pigment is stimulated.
Primates have three different pigments, producing trichromatic
Anthropoid vision is stereoscopic;
that is, the eyes are positioned forward, allowing an overlap
of most of the fields of vision with the optic axes parallel.
An object is focused on both retinas simultaneously. The optic
nerve tracts that pass information from retina to the brain meet
at the optic chiasma. In most vertebrates and marsupials the fibres
of the optic nerves cross at the chiasma and pass to the opposite
of the brain. However in mammals, some of the fibres do not cross
over so information from each eye is processed on both hemispheres
of the brain(return to outline).
The murder of George Parkman, M.D.,
in 1849 stimulated Oliver Wendell Holmes, Dean of Harvard Medical
College, and Professor Jeffries Wyman, an anatomist at Harvard,
to formulate a protocol for investigating fragments alleged to
be from a cadaver found at the murder scene (Joyce and Stover,
1991; page 52):
1. Are the remains human?
2. Do they represent a single individual or the commingled remains of several?
3. When did death occur?
4. How old was the decedent?
5. What was the decedent's gender?
6. What was the decedent's race?
7. What was the decedent's stature?
8. Did the body exhibit any significant anomalies, signs of disease and injuries, or other characteristics sufficiently out of the ordinary to provide positive identification?
9. What was the cause of death?
10. What was the manner of death? (natural, accidental, homicide, suicide, or unknown)
This is pretty close to the list
of questions that a modern forensic investigator would ask. Two
cardinal rules must be added: 1) Maintain tight security and record
keeping so there is no lapse or break in the chain of evidence
that may be later used in court. 2) Follow carefully planned procedures
so there is no loss of evidence or information. The material is
usually determined to be human or not on the basis of the scientists'
familiarity with human anatomy. If a burial site, an anthropologist
or archaeologist may be asked to determine whether it is current
or prehistoric. The first stages of investigation may be tedious
excavation, using careful archaeological techniques to expose
the material and recover all evidence. Normally the skeleton is
fully exposed and carefully photographed in situ. If it
is a body, degree of decomposition, type of insects present, and
characteristics of the site may provide information about the
length of time since burial.
Excavated material will be carefully
packaged, transported to the laboratory, cleaned, and placed on
a table in approximate anatomical position. The question of how
many individuals are represented is answered by careful examination
of the skeletal elements present. If there are a large number
of bones and there are no repetitions (such as two right femurs),
then it is unlikely that more than one person is present. The
theoretical maximum number is the number of bones present (since
each could have come from a different individual) and the theoretical
minimum is the number of individual elements that are duplicated
(two left femurs = two individuals). In addition to counting skeletal
elements, each bone must carefully examined to determine if size,
age, gender, and other characters coincide with interpretation
of what constitutes an individual(return
the Age of the Individual
Age estimates are readily made from
dental eruption. Dental attrition and dental loss may indicate
older age categories among adults. Severe tooth wear is commonplace
in prehistoric individuals. Skeletal maturation of epiphyses to
diaphyses is an accurate guide to age. Though cranial suture closure
is more variable, is useful for older age ranges). Many areas
of the older adult skeleton undergo progressive deterioration
that serves as useful indicators of age. The pubic symphysis and
sternal ends of ribs are particularly useful. As living bone ages,
there is a slight but cumulative loss of osteons, microscopic
circular structures of bone that surround a haversian canal(return to outline).
the Gender of the Individual
A scientist working with a large
sample of skeletons from a localized deme would be able to distinguish
gender groups on the basis of size and robusticity. Males are
5-10% larger, heavier and more rugged. Females as a group tend
to be more gracile and have finer muscle markings. However, when
dealing with a single specimen from an unknown background, it
is difficult to calibrate the judgment of what is large or robust.
Further, it is extremely difficult to make accurate gender estimates
on immature specimens since many distinguishing characters are
evident only after adolescence. Size alone is always a risky guide.
The most dramatic differences between
males and females are in the pelvis where sexual dimorphism reflects
the compromise between childbirth and locomotion. Since the heads
of the humerus and femur reflect body size, the diameter of these
two features provides a crude but convenient guide:
< 41 mm = female
> 45 mm = male
A similar relationship works for
the foot. If the maximum length of the os talus is greater than
52 mm, the individual is likely to be male.
The skull is often used as a guide
to gender. Males tend to have larger and more robust faces, especially
the supraorbital torus. If the upper border of the orbit has a
knife-like margin, the individual is likely to be female. A large
mastoid process is a male indicator. The male mandible tends to
be larger, with an outward flaring gonial angle and a square chin.
A female chin is more pointed.
The gender of a pelvis is recognizable
in 90% of individuals by the ratio of the length of the ischium
divided by the length of the pelvis (Washburn, 1948). A value
greater than .9 indicates female (return
the Race of the Individual
The Office of Management and Budget
has established a classification that is used in reporting federal
statistics (Hoyme and Iscan, 1989). These categories are also
likely to be used in law enforcement records and reports, but
they represent bureaucratic categories, not scientific or anthropological
1. American Indian or Alaskan native
2. Asian or Pacific Islander
Since American Indians are derived
from Asian populations, it would require exceptional efforts and
circumstances to distinguish between the first two groups. Likewise,
many Hispanics have American Indian ancestry. Ethnic group is
usually defined culturally and generations of immigrants to this
country are not inhibited by geographic isolation from marrying
persons from other groups. Consequently the forensic scientist
must be very conservative. Usually the decisions are made on the
basis of dichotomies such as "Asian/not Asian" or "Black/not
Black". For example, presence or absence of shovel-shaped
incisors would imply Asian or not Asian respectively (return to outline).
A useful technique of estimating
gender or biological affinity has been to examine cadavers of
known age and background to develop measurements and computations
that correctly distinguish gender and population differences.
Unfortunately study samples tend to be from unusual populations
(such as the unclaimed bodies from the morgue or bodies donated
for medical dissection). Since it is very questionable that most
such samples are comparable to present populations, such statistics
are used only as a supplement or aid in estimation.
A scientist uses a discriminate function
by taking the appropriate measurements carefully to the nearest
millimeter. Each measurement is then multiplied by a coefficient
specified in the function formula, and the computed products are
added or subtracted (according to their sign). If this sum is
above the value specified as sectioning point for that computation,
the decision is yes, the estimate indicates membership in the
group specified by that equation. For example the following formulas
distinguish, with about 75% accuracy, between American Blacks
and American Whites using measurements of the pelvis (Iscan, 1983).
Bi-iliac breadth(0.637219)-16.84043 = score
Transverse breadth (0.1303004)-15.34591 = score
Bi-iliac breadth(0.0604552)-16.0448 = score
Transverse breadth(0.1336859)-17.01109 = score
A score greater than zero indicates
American white, the group whose pelvis is usually slightly larger
(return to outline).
of Stature of the individual
Regression formulae have been devised
from cadaver samples for estimating stature from measurements
of long bones. The length of the bone (measured in cm) is substituted
into an appropriate equation (after Trotter, 1970).
For White male
2.38(femur length) + 61.41 = stature
+ 3.27 cm
For White female
2.47(femur length) + 70.35 = stature
+ 3.94 cm
For Black male
2.11(femur length) + 86.02 = stature
+ 3.94 cm
For Black female
2.28(femur length) + 59.76 = stature
+ 3.41 cm
(return to outline)
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