Types of bone

Outline:
Types on the basis of shape:

  1. Long bones,
  2. Short bones,
  3. Flat bones,
  4. Irregular bones,
  5. Pneumatic bones,
  6. Sesamoid bones

Types on the basis of development:

  1. Membranous bones,
  2. Cartilaginous bones,
  3. Membro-cartilaginous bones

Types on the basis of region:

  1. Bones of axial skeleton,
  2. Bones of appendicular skeleton

Types on the basis of structure:
According to Macroscopic approach;

  1. Compact bone,
  2. spongy bone

According to Microscopic approach:

  1. Fibrous bone,
  2. Lamellar bone

Types of bone

Human bones are classified on different bases of classification. Generally four types of classifications are followed each dividing bones into different types.

Types of bone on the basis of shape:

On the basis of shape, bones are classified into seven different types;
Long bones:
These bones typically have an elongated shaft and two expanded ends one on either side of the shaft. The shaft is known as diaphysis and the ends are called epiphyses. Normally the epiphyses are smooth and articular. The shaft has a central medullary cavity where lies the bone marrow. Long bones are further divided into three categories that are;

Typical long bones: They have an elongated shaft and two ends and are represented by bones such as humerus, femur, radius, ulna, tibia and fibula.

femur

Femur

Miniature long bones: As the name indicates, these bones have a miniature appearance and often they have only one epiphysis. Examples of this class of long bones are metacarpals, metatarsals and phalanges of both upper and lower limb.

Third metacarpal bone

Third Metacarpal Bone

Modified long bones: These bones either have modified shaft or ends. They have no medullary cavity which is present in the typical long bones. Examples of this class of bones are clavicle and body of vertebrae.

Clavicle

Clavicle

Short bones:
These bones are short in posture and can be of any shape. Most of them are named according to their shape. Examples of this class of bones include cuboid, cuneiform, scaphoid, trapezoid etc. In fact all the carpal and tarsal bones are included in this category.

Carpal Bones

Carpal Bones

Flat bones:
These bones are flat in appearance and have two prominent surfaces. They resemble shallow plates and form boundaries of certain body cavities. Examples include scapula, ribs, sternum etc.

Scapula

Scapula

Irregular bones:
The shape of these bones is completely irregular and they do not fit into any category of shape. Examples of this type of bones are vertebrae, hip bone and bones in the base of skull.

Hip Bone

Hip Bone

Pneumatic bones:
Pneumatic bones can also be categorized under the irregular bones because they are also irregular in shape but since there is a difference between the two that is characteristically very important therefore they are often classified separately. The characteristic difference is the presence of large air spaces in these bones which make them light in weight and thus they form the major portion of skull in the form of sphenoid, ethmoid and maxilla. Besides making the skull light in weight they also help in resonance of sound and as air conditioning chambers for the inspired air.

Paranasal Sinuses Showing Skeletal Pnumatization

Paranasal Sinuses Showing Skeletal Pnumatization (Source: M.Komorniczak/Wikipedia)

Sesamoid bones:
These are not like the other types of bones because they are in the form of nodules embedded in tendons and joint capsules. They do not possess any periosteum and their ossification also takes place after birth. Examples of this type of bones are patella, pisiform and fabella.

Patella

Patella

Types of bone on the basis of development:

On the basis of the pattern of development a bone follows, there are three categories which are described in detail below;
Membranous bones:
These are also known as dermal bones and the process by which they ossify is called intra-membranous ossification. These bones ossify from mesenchymal condensations in the intrauterine life. Examples are bones of the skull and facial bones.

Bones of Skull and Face

Bones of Skull and Face

Cartilaginous bones:
These bones ossify from a cartilage model and this type of ossification is known as intra-cartilaginous ossification. These bones do not form from mesenchymal condensations but from preformed cartilage models. Examples of this type of bones include bones of limbs, vertebral column and thoracic cage.

Appendicular skeleton showing bones of limbs

Appendicular skeleton (in red) showing bones of limbs

Membrocartilaginous bones:
These bones ossify partly from cartilage and partly from mesenchymal condensations. Examples of this class of bones include clavicle, mandible, occipital, temporal and sphenoid etc.

Types of bone on the basis of region:

On the basis of region we have two types of bones that are
Bones of axial skeleton:
These bones form the axial skeleton of human body. Examples are bones of skull, vertebral column and thoracic cage.

Axial Skeleton

Axial Skeleton (in blue)

Bones of appendicular skeleton:
These bones form the appendicular skeleton of the body. Examples of this type of bones are bones of the limbs and girdles of limbs.

Appendicular skeleton showing bones of limbs

Appendicular skeleton (in red)

Types of bone on the basis of structure:

As discussed in the start of the page, 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. The structural classification has two approaches that are macroscopic approach and microscopic approach.
Macroscopic approach divides the bones into two categories that are;
Compact bone:
The part of a bone where bone substance to bone space ration is a bigger quantity is called compact bone. This means that there is more bone tissue and less empty space.
Spongy bone:
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.

Compact and Spongy bone

Compact (outer) and Spongy (inner) parts of bone

Microscopic approach divides the bones into following categories;
Lamellar bone:
The type of bone which are composed of thin plates (lamellae) of bony tissue. Most mature human bones are lamellar bones.
Fibrous bone:
These have more fibers in them. In humans they are found only in fetus.
For detailed anatomy of bone, visit [intlink id="bone" type="page"]Bone[/intlink]