- Skeletal system constitutes hard internal or
external living or non-living parts that form
the supporting framework of body.
- It is divided into 2 parts.
- Exoskeleton: Which is produced by
ectoderm. It is present on the outside of the
body (made of either dead tissues or
biochemical secretion). Found in both
invertebrates and vertebrates
- Endoskeleton: Which is produced by
mesoderm. It occurs inside the body and is
made of cartilages and bones.
- Divided into two main parts: Axial Skeleton
and Appendicular Skeleton.
A. AXIAL SKELETON (Total 80 bones) SKULL
- Skull consists of two main parts cranium and
- Cranium (brain box) is formed by 8 bones
and provides a bony protection for the brain.
- Face: There are 14 bones which form the
skeleton of face.
- There are also present 6 ear ossicles in the
- Another bone is hyoid.
- It is made up of 33 vertebrae in which 26
bones are visible because five sacral
vertebrae are fused to form one sacrum and
four coccygeal vertebrae are fused to form
- Ribs are 12 pairs (12 x 2) of bony bars which
form the sides of chest cage. They protect the
delicate organs (heart, lungs, etc)
STERNUM or Breast Bone
- It is a narrow, elongated and flattened
- structure, present just under the skin in the
middle front of the chest.
B. Appendicular Skeleton (Total 126 bones)
- This skeleton lies laterally and is attached to
axial skeleton at an angle. It is made up of
girdles (pectoral and pelvic) and limb bones
(forelimb and hindlimb)
- Shoulder girdle
- Has 4 bones (two in each pectoral girdle)
- Forelimbs – Consists of 60 bones.
- Hindlimbs – Consists of 60 bones.
Femur (2) – Thigh (longest bone in the
Fibula (2) – Shank (thinnest bone)
PELVIC GIRDLE – Has 2 hip bones
DISEASES OF SKELETAL SYSTEM:
- Gout:Accumulation of uric acid crystals in joints
leading to painful movement.
- Dislocation: In this case, the bones at the joints
are dislodged from their positions e.g., the ball of
one bone may slip out of the socket.
- Hard tissue deposits over articular cartilage along
with higher secretion of synovial fluid causing pain
and stiffness lead to rheumatoid arthritis.
- Tearing of articular cartilage nd development of
bony lumps at places causing pain, stiffness and
permanent bending lead to osteoarthritis.
- Bursitis is inflammation of the bursae present
within synovial joint as small membrane bound
pockets which stores synovial fluid.
- Osteitis is inflammation of bone.
- Osteoporosis is loss of bone density due to
excessive absorption of calcium and phosphorus
from the bone.
- Osteomyeliltis is infection of bone.
- Osteopetrosisis a hereditary disease marked by
abnormally dense bone, and by the common
occurrence of fractures of affected bone.
ARTICULATION OF BONES – THE JOINTS
- A bone joint or articulation may be defined
as the junction of two bones. The study of
such joints is known as arthrology.
- Femur (in hind limbs) is the longest bone
and stapes (in middle ear) is the smallest
bone of the body.
- Sternum is absent in fish.
- Fibulla – thinnest bone
- Osteology is study of skeleton.
- Chondrology is study of cartilages.
- Arthrology is study of joints.
- Masseters of jaw is the strongest muscle.
- Birds have spongy bones with air filled
spaces, called pneumatic bones.