classification of bones

2. Classification of bones on the basis of regions
On the basis of regions, the bones are classified into:
(1) Bones of axial skeleton
(2) Bones of appendicular skeleton

3. Axial skeleton
Skull
Cranium 8
Face 14
Auditory Ossicles 6
Hyoid 1
Sternum 1
Ribs 24
skull total 54
Vertebrae
Cervical 7
Thoracic 12
Lumber 5
sacrum 1
coccyx 1
Vertebrae Total 26
Total 80

4. Appendicular skeleton
Shoulder girdles
Clavicle 2
Scapula 2
Upper extremities
humerus 2
radius 2
Ulna 2
Carpals 16
Metacarpals 10
Phalanges 28
Upper extremities total 64
Pelvic girdle
hip bone 2
Lower extremities
Femur 2
Patella 2
Fibula 2
Tibia 2
Tarsals 14
Metatarsals 10
Phalanges 28
Lower extremities 62
Total 126

5. Classification of bones on the basis of shape
On the basis of shape, the bones are divided into eight types:
Long bones
Short bones
Flat bones
Irregular bones
Sesamoid bones
pneumatic bones (hollow)
accessory bones (confused)
heterotrophic bones ( the abnormal growth of bone)

6. (1) Long bones
Their length is greater.
They are found in the limbs.
They have a tubular shaft (diaphysis)and usually
an expanded epiphysis (pineal.) at each end.
Each shaft has three surfaces (posterior, medial
and lateral ) separated by three borders.
The shaft has a central marrow cavity
containing bone marrow.
Examples: Femur, Humerus, Radius,
metacarpals,metatarsals and clavicle etc.

7. (2) Short Bones
Short bones are found in the hand and foot. They are roughly
cuboidal in shape and are composed of cancellous bone surrounded by a
thin layer of compact bone (cortical bone). Short bones are covered with
periosteum (a dense layer of vascular connective tissue), and the articular
surfaces are covered by hyaline cartilage.
Examples:
scaphoid, lunate, talus, and calcaneum etc.

8. (3) Flat Bones
Flat bones resembles shallow plates and form boundaries of certain
body cavities.
They are found in the vault of the skull (e.g., the frontal and parietal
bones). They are composed of thin inner and outer layers of compact
bone, separated by a layer of cancellous bone,
Examples:
Bones in the vault of the skull, ribs, sternum and scapula.

9. (4) Irregular Bones
These bones are irregular in shape.
They are composed of a thin shell of compact bone with an
interior made up of cancellous bone.
Examples:
The bones of the vertebrae and the pelvic bones.

10. (5) Sesamoid Bones
Sesamoid bones are small bones that are found in certain
tendons where they rub (massage)over bony surfaces.
They ossify after birth.
The function of sesamoid bones are to resist pressure, to
minimize friction, to alter the direction of pull of the
muscle and to maintain the local circulation.
The greater part of a sesamoid bone is buried(‫)دفنانا‬ in the
tendon, and the free surface is covered with cartilage.
The largest sesamoid bone is the patella. Other examples
are pisiform .

11. (6) Pneumatic Bones
Certain irregular bones contain large air spaces lined by
epithelium. They make the skull light in weight, help in
resonance of voice, and act as air conditioning
chambers for the inspired air.
Examples:
maxilla, sphenoid, ethmoid, etc.

12. (7) Accessory bones
These are not always present.
These may occur as ununited epiphysis developed from extra
centres of ossifications.
Examples:
sutural bones, os trigonum (lateral tubercle of talus), etc.
(8) Heterotrophic bones
These bones sometimes develops in soft tissues.
Horse riders develops these bones in adductor(‫واال‬ ‫کرنے‬ ‫)نشہ‬ muscles
(rider’s bones)

13. Developmental Classification of Bones
(1) Membranous (Dermal) Bones
These types of bones ossify in membranes
(intramembranous ossification).
These bones ossify from mesenchymal condensations in
the intrauterine life.
Examples:
Bones of the skull and facial bones.

14. (2)Cartilaginous
Bones
These types of bones
ossify in cartilages
(endochondral
ossification) and are
thus derived from
preformed cartilaginous
models.Examples:Bones
of limbs,vertebral
column and thoracic
cage.
(3) Membrano-
Cartilaginous Bones
These ossify partly
in membrane and partly
in cartilage.
Examples: clavicle,
mandible, occipital,
temporal, sphenoid.

15. Types of Bones Based on Bone structure
All bones are composed of same material. The difference only is in
the pattern of arrangement. This classification is based on the same
thing that is pattern of arrangement of bony tissue. It has two types
of classifications
Macroscopic classification
It has two types,
(1) compact bones (2) spongy bones

16. (1) compact bones
Compact bone is also called cortical bone.Shaft of bone in a long
bone like femur is typical example of the compact bone.
Compact bone forms the cortex, or outer shell, of most bones.
It is much denser, harder, stronger and stiffer.
Compact bone contributes about 80% of the weight of a human skeleton.
Compact bones are arranged for the following functions
To support the whole body weight
Protect organs
Provide level for movement.
Store and release calcium.

17. (2) Cancellous or Spongy or trabecular bone
These are open in structure.
The part of a bone where bone substance to bone space ratio is
a smaller quantity. This means that there is more empty space
and less bone tissue.
Compared to compact bone, it has a higher surface area but is
less dense, softer, weaker, and less stiff.
It typically occurs at the ends of long bones, proximal to joints
and within the interior of vertebrae.
spongy bone is highly vascular and frequently contains red bone
marrow where production of blood cells occurs.

18. Microscopic classification
(1) Lamellar bone
The type of bone which are composed of thin plates of bony tissue
(lamellae). Most mature human bones are lamellar bones.
(2) Fibrous bone
These have more fibers in them. In humans they are found only in
fetus.
Some other less important microscopic bones are
woven bones, seen in fetal life, in fracture repair and in cancer
condition.
Dentine and cement occurs in teeth.