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Skeletal system



Skeletal system


General:
  • There are 206 bones in an adult human body. Bones of hands and feet constitute 50% of the total bones in the body.
  • A new born baby has 300 bones. 96 of these fuses together with growth.
  • The largest bone of the body is the FEMUR. It is the thigh bone. It constitutes of about 27.5% of a person’s stature. The average length of FEMUR is 50cm.
  • The shortest bone of the body is the STAPES or STIRRUP in the middle ear.
Function of the bones:
  1. They are the connective tissue of the body.
  2. Muscles attach to the bones. The bones act as levers for muscles to work.
  3. Skeletal system provides shape to the body.
  4. Protect the internal organs of the body.
  5. The bone marrow (in the long bone) produces RBCs.
Important bones:
Skull bones (cranium) : skull is formed of 8 bones.
Bone NameNumber
frontal (forehead)1
parietal (side of the head)2
occipital1
temporal2
sphenoid1
ethmoid.1
Facial bones: facial bones consist of 14 bones. They are joined by immovable joints except for the lower jaw bone (mandible)
Facial bones are as follows:
Bone nameNumber
Lachrymal2
Os- Nazale (Zygomalicum)2
Cheek bone2
Vomer1
Sponge bone2
Palate bone2
Super Maxillary2
Mandible2

Upper extremities:
NameNumber
Shoulder bone
Scapula (triangular shaped)2
Clavicles2
Bones of arms
Humerus (largest bone of the arm)1
Radius (outer bone)1
Ulna (inner bone)1
Carpals8
Meta carpal (middle hand)5
Phalanges14
Backbone (spine) : also called the vertebrae, it encloses the spinal cord. In childhood the backbone consists of 33 separate bones. While in adult there are 26 separate vertebrae (rest fuse together).
The vertebral column is sub-divided into 5 regions.
RegionNumber of bones
Cervical (neck bone)7
Dorsal (rib support)12
Lumber (backbone)5
Sacrum5 (25th to 29th fused together)
Coccyx (tail bone)4 (fused together in adults)
The thorax is a protective casing for the lungs and heart. It consists of a sternum and 12 pairs of ribs.
  1. Hip bone: Consists of 3 bones: Ilium, Ischium and Pubis. In mature adult these bones fuse to become one. It is then called as Os Coxae or the Hip bone.
  2. Bones of the leg:  Each leg consists of 30 bones.
They are:
Bone nameNumber
Phalanges (toe bone)14
Tarsal (ankle bone)7
Femur (thigh bone)1
Tibia (shin bone)1
Fibula (calf bone)1
Patella (knee cap)1
Composition of bones :
  1. Organic matter      33%
  2. Phosphate lime     51.04%
  3. Carbonate lime     11.3%
  4. Fluoride of Calcium          2%
  5. Phosphate of Magnesia    1.16%
  6. Soda/Chloride of sodium  1%
Bones consists of 80% solid matter and 20% water.  Impregnation of bones with salts including that of carbonates and phosphate hardens the bone. In old age the proportion of lime decreases making the bone brittle and prone to fracture.