Chapter 7
The Skeleton
J.F. Thompson, Ph.D. & J.R. Schiller, Ph.D. & G. Pitts, Ph.D.
Divisions of the Skeleton
I.
Axial skeleton
A.
B.
long axis of the body
skull, vertebral column, rib cage
II. Appendicular skeleton
A.
B.
appendages and connections
upper, lower limbs, pelvic, pectoral girdles
Know the Features Outlined in Your Lab Guide.
The Skeleton
Know the Features Outlined
in Your Lab Guide.
The Adult Skeleton
The Fetal Skeleton
The Fetal Skull
Intramembranous ossification with sutures fusing late so
the skull bones can expand to accommodate significant
brain growth.
The Fetal Skull
Intramembranous ossification with sutures fusing late so the skull
bones can expand to accommodate significant brain growth.
Body Part Growth Rates
Trunk and limbs develop more slowly than cranium and
face.
Human Body Form Varies Geographically
Humans adapted to cold climates often have
thick trunks and shorter limbs; those adapted to
warm climates tend to be taller and slimmer.
a)
b)
Inuit from the Arctic
(under five feet tall).
Nilote of near
equatorial Africa
(over six feet tall).
Modern Human Regional Variation
African
European-SW Asian
East Asian
Australian
Humans Are Bipedal Apes
Apes are large tailless omnivorous
primates with relatively large brains
and complex social behaviors.
Apes evolved in Africa and Asia and
most live in moist tropical forests.
The Living
Apes
Anatomical striking resemblance
Asia
Africa
now global
Comparison of Human and Ape Skeletons
Non-human apes
are quadrupeds
Human –
Gorilla
– Chimpanzee – Orangutan - Gibbon
Comparison of Human and Ape Skeletons
The differences in the skeletons of the apes are primarily
differences in proportions of bones reflecting different
styles of locomotion, different diets, and intelligence.
The Major Morphological Trends
I.
Larger brain; taller, flatter face; smaller jaws and
teeth, and structural adaptations for making the
sounds of speech.
Most of the
differences
between
Humans and
Apes are
adaptations to
walking
bipedally.
1. foramen magnum
2. spinal double
curvature
3. pelvic architecture
4. femur angle
5. weight-bearing knee
6. double arched foot
Brief Survey of the Human Skeleton
We emphasize the changes between bipedal
humans and the other quadrupedal apes.
The shift to bipedalism, while advantageous
to human success, also has many negative
consequences.
Many of these differences have clinical
significance.
Anatomy of the Lateral Aspect of the Skull
Know the Features Outlined in Your Lab Guide.
diastemas
Anatomy of the Anterior Aspect of the Skull
interlocking canines
The human
Canine
Usually no
Teeth are
diastemas (gaps)
especially
between teeth.
reduced
compared
to Apes to permit rotational chewing.
Dentition
Chimpanzee incisors
tip forward to grasp
and mash soft fruit
Reduced human canines aligned with the
incisors form a cutting blade for tougher
plant and animal foods.
Dentition
Diastemas develop as
the jaws of an ape
grow anteriorly
Anatomy of the Lateral Internal Aspect of the Skull
Know the Features Outlined in Your Lab Guide.
The Forehead is taller.
The human
Cranium is
much enlarged
compared to
apes.
chimpanzee
The human face is
much Flatter.
Anatomy of the Inferior Portion of the Skull
The Dental Arch is broader and more rounded than in apes
chimpanzee
mandible →
Anatomy of the Lateral Aspect of the Skull
The human Palate is arched which gives greater
variety to tongue shapes to articulate speech.
Changes in the Palate and Dentition
Note arches, canine sizes, diastemas, incisor sizes and molar sizes.
Anatomy of the Inferior Portion of the Skull
Know the Features Outlined in Your Lab Guide.
The Foramen
Magnum is
centered under the
expanded brain,
compared to apes,
for erect posture.
Detailed Anatomy of Some Isolated Facial Bones
Humans have a
distinct chin
and the
attachment of
the tongue
behind the chin
allows for more
varied tongue
movements
necessary to
articulate
speech sounds.
chimpanzee
mandible
Compare
Forehead height, flatness of face, prominence of chin;
note the differences are less pronounced in the infants.
Why Have Air-Filled Sinuses in the Skull?
Paranasal Sinuses: Anterior Aspect
Probably Vestigial Structures – sites for additional
Olfactory Epithelium in ancestral species.
As resonating chambers,
give distinct timbre to
each human voice.
The Vertebral Column
Know the
Features
Outlined in
Your Lab
Guide.
Note the Double
Curvature of the
Spine.
It is an
Adaptation for
Upright Posture.
Apes (and
human
neonates)
have a single
curve.
Note the Complex Set of Ligaments
And the Intervertebral Discs
Posterolateral Views of Articulated Vertebrae
Much of the rotation of the head occurs at the joint
between the atlas (C1) and dens of the axis (C2).
Intervertebral Disc
surrounded by
the meninges
normal
degenerate
fibrocartilage
gelatinous remnant of
the notochord
Regional Characteristics of Cervical, Thoracic, and Lumbar Vertebrae
Key Differences Among Vertebral Types:
For
Blood
Vessels
Size
Of
Body
Facets
for Rib
to
Attach.
No
Facets
for Rib
to
Attach
The Bony Thorax
Like other apes,
Humans have a
broad but
Shallow rib cage,
an adaptation to
Brachiation
The Bony Thorax
CPR:
The position of
the heart beneath
the sternum
permits the CPR
technique to pump
blood when the
heart has ceased
to pump on its
own.
Bones of the Appendicular Skeleton: Pectoral Girdle and Upper Limb
Know the Features Outlined in Your Lab Guide.
*
* Greater
Opposability of the
thumb is the main
difference between
the human and
the ape arm.
Forelimb: the pectoral girdle is
adapted for braciation in apes
and humans
*
* Greater
Opposability of the
Thumb is the Main
Difference Between
the Human and
the Ape Arm.
Manual Dexterity
Compare relative finger
lengths and note the
opposability of
the thumbs.
The Size of the Angle of the Pubic Arch and of the
Greater Sciatic Notch are the Best Gender Markers.
Humans and Human Ancestors
Are Fundamentally Bipedal Apes.
Curved femurs allow feet
to be placed together; a
larger hip joint can bear
more body weight
Bones of the Right Foot
Compared to the
ape’s foot, the
human foot is
entirely changed
and adapted to
Bipedal Locomotion;
there is no
opposability of the
big toe.
Arches of the Foot
The Double Arch Design
is an Adaptation to
Bipedal Locomotion,
walking and running.
Comparison of Hominoid Pelves and Feet
Changes accommodate muscle attachments for bipedal locomotion.
Hip Mechanics and Locomotion
Hip Mechanics
and Birth Canal
Compare the Bonobo and
Human females.
The human waist seems narrow
because the hip (coxal) bones
have grown wider and the
gluteal muscles have grown
larger.
An Australopithecine would be
intermediate in architecture, but
fully bipedal and a bit more
efficient at walking!
Ape and Hominid Skeletons
I.
II.
III.
Respectively, the backbone joins the back of the skull in apes versus the
bottom.
The ape backbone is arched while the hominid is S-shaped.
The arms are long in both, but shorter than hindlimbs in the ape compared to
the hominid.
Comparison of Ape and Human Posture
Approximate Timeline
for Human Prehistory
1. Ardipithecines: 5 to 4.5 mybp
2. Australopithecines: 4.5 to 1.2 mybp
3. Homo erectus: 2.0 to 0.5 mybp
4. Archaic Homo s. sapiens and Homo
sapiens neaderthalensis: 500,000 200,000 years
5. Modern Homo s. sapiens: the last
200,000 years
Ardipithecines
• Two fossil species
from 5 to 4.5 mybp
• Among the earliest
forms in the human
ancestry
• Anatomical traits
suggest a
combination of
arboreal and bipedal
locomotion
“Ardi” was smaller (1.2 m) and
less anatomically specialized
than modern chimps or gorillas
Ardipithecines
• A “missing link” that is not missing!
• Less specialized than a chimpanzee
chimp-like
ancestral,
intermediate
human-like
Australopithecines
• Several fossil species
from 4.5 to 1.2 mybp
• Anatomical traits
suggest the completion
of the transition to
bipedal locomotion
• Brain size, behavior
and social organization
roughly comparable to
modern chimpanzees
“Lucy” A. afarensis
Australopithecus afarensis
I.
II.
III.
a reconstruction of “Lucy’s”
skeleton
adaptations in “Lucy’s” hip, leg
and foot allowed a fully bipedal
means of locomotion
other adaptations of the fingers
and toes suggest considerable
ability brachiation in the trees
The transition to bipedal
locomotion occurred at
least 5 million years ago,
while the increase in
cranial capacity is a
much later development,
from less than 2 million
years ago.
Australopithecus africanus
The Major Morphological Trends
Homo erectus
• Major Homo erectus changes:
–
–
–
–
–
–
–
Brain size
Hunting
Fire
Tool cultures
Built shelters (H. heidelbergensis)
Clothing (H. neandertalensis)
Language when?
Skulls
(a) Homo erectus; (b)
a modern human,
Homo sapiens.
II. In H. erectus, note
the prominent brow
ridges (open arrow)
and their absence in
H. sapiens.
III. Chin (solid arrow) is
recessed in H.
erectus, and
protruding in H.
sapiens.
I.
Brain Expansion Came Last
Did language and
complex social
behaviors drive
brain expansion?
Variation in Body Hair (When?)
Could body hair shorten until bipedalism freed the hands to carry the baby?
Some Clinical Consequences of Bipedalism
1.
2.
3.
4.
5.
6.
7.
8.
abnormal spinal curvatures
herniated disks
joint problems at the hip, knee and ankle
problems with the arches of the feet
bunions
osteoporosis of the spine and lower limbs
difficult labor and delivery
hernias
Trauma to the Face
During a softball
game, another
player’s elbow
collides with my
friend’s face, just
below the eye.
On x-ray, the
Blood collected
in the Maxillary
Sinus cavity was
visible.
On x-ray,
the fracture
of the
Zygomatic
Arch is
obvious.
The impact
fractured
Dave’s nose
as well.
Trauma to the Elbow
Wires were
surgically
implanted
To repair a
fracture of
the Olecranon
Process.
End Chapter 7
Skeletons of Our Ancestors from 5-4 Million Years Ago:
Australopithecus afarensis (left) and Australopithecus
robustus (middle) compared to H. sapiens (right)