2. 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:
3. 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.
4. 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.
5. 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.
6. 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.
7. 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
8. 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.
9. 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.
10. 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.
