Skeletal system
This system is made up of hard tissues like bone and cartilages. This system gives form
and shape to animal body The skeleton of a living animal is made up living structures of
bones. The bones have blood vessels, lymphatic vessels and nerves. They are subject to
disease, repair themselves and adjust to changes during stress.
Functions of Bones:
• Protection: protection of some vital organs from the external damages is one of
the important functions of bones. The central nervous system (CNS) is
protected by the skull and vertebral column; the heart and lungs by rib cage;
and pelvis protects the internal parts of urogenital system.
• Rigidity and form to the body: animals without a skeleton of some type have
little or no regular form. The skeleton gives a basis for the external structure
and appearance of most animals.
• Act as lever: in the vertebrates, locomotion, defense, offense, grasping, and
other activities of this type depend largely upon the action of muscles that are
attach to the levers. Almost without exception, these levers are made of bone
and are integral parts of skeleton.
• Storage of minerals: the entire skeleton serves as a dynamic storage area for
minerals, particularly calcium and phosphorous. These minerals are deposited
and withdrawn as needed in the on-going homeokinetic process.
• Site for blood formation: blood formation is not strictly a function of bone
proper, but of the marrow found within the marrow cavity of long bones and
within the spongy substance of all young bones.
Classification of bones
Any bone may be classified into one of the following groups:
Long bones: are relatively cylindrical in shape with two extremities called epiphyses (see
Figure ). There is metaphysis between each epiphysis and the diaphysis. A long bone
grows in length only at the epiphyseal cartilage which is located within the metaphysis.
Epiphysis
Diaphysis
Metaphysis
Medullary
Cavity
Metaphysis
Epiphysis
Figure 7: longitudinal section of the humerus of a mature dog.
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Function of long bones: chiefly as levers and aid in support, locomotion and prehension.
The best examples of long bones are pectoral limb, humerus, radius, ulna, metacarpals,
phalanges; pelvic limb, femur, fibula, tibia, metatarsals and phalanges.
Short bones: are somewhat cuboid in shape i.e approximately equal in all dimensions.
There is no marrow cavity. They are found in complex joints such as the carpus (knee)
and tarsus (hock). Example of short bones: Patella.
Function: - for variety of movement
- absorption of shock
Flat bones: are relatively thin and expanded in two dimensions. They consist of two plats
of compact substance, lamina externa and lamina interna, separated by diploe. Example
of flat bone: frontal base of skull, scapula and pelvic bones
Functions: - protects vital organs such as brain, the heart and lungs.
- many provide large areas for muscle attachment.
Sesamoid bones: they are developed along the course of tendons. Example: Patella (knee
cap) is the largest sesamoid in the body.
Functions: - reduces friction or change the course of tendons.
- may change the angle of the pull of muscles and this give a greater
mechanical advantage.
Phunumatic bones: they contain air spaces or sinuses that communicate with the exterior.
Example: long bones of bird, frontal bones and maxillary bones of the skull.
Irregular bones: are unpaired bones located on the median plane and include the
vertebrae and some of the unpaired bones of the skull.
Functions: - protection, support and muscle attachment.
For better understanding the skeletal system can be divided into two parts viz the axial
skeleton and appendicular skeleton.
Axial skeleton: is made up of skull, and vertebral column sternum and ribs. The table
below indicates the bones of the axial skeleton by regions.
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Table: Bones of the Axial skeleton system. (Source: Spurgeon, 1992)
Skull
Vertebrae
Cranial bones
-occipital
- parietal
- interparietal
- temporal
- frontal
- ethmoid
- sphenoid
cervical
thoracic
lumbar
sacral
caudal
Facial bones
- pterygoid
- lacrimal
- nasal
- palatine
- conchae (turbinates)
- maxilla
- incisive (premaxilla)
- zygomatic (malar)
Vomer
Mandible
Hyoid
Ribs
True ribs -join sternum by costal
cartilages
False ribs- not directly connected
with sternum
Floating ribs- last 1 or 2 pair
connected only with vertebrae
Sternum
manubrium
body
xiphoid process
Skull: forms the basis of the head. It consists of cranial bones, which surround the brain
and facial bones, which exhibits observable variation among the species.
Function: - protection of brain
- Supports many sense organs
- Forms passage for the beginning of digestive and respiratory system
Vertebral column: composed of median, unpaired and irregular bones. The following
indicates the part of vertebral column and letters are used to designate the respective
regions.
• Cervical vertebrae (C) - neck region
• Thoracic or dorsal (T) - chest region
• Lumbar (L) - loin region
• Sacral (S) - in region of pelvis- fused vertebrae
• Fused Lumbar and Sacral (LS)- in fowl
• Caudal or Coccygeal (Cd) - located in tail
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Vertebral formula: for a given species consist of the letter symbol for each region
followed by the number of vertebrae in that region in the given species. The following
shows the vertebral formula of common farm animals.
Cow: C7 T13 L6 S5 cd18-20
Sheep: C7 T13 L6-7 S4 cd16-18
Pig: C7 T14-15 L6-7 S4 cd20-23
Horse: C7 T18 L6 S5 cd15-20
Chicken: C14 T7 LS14 cd6
Sternum and Ribs: forms the floor of the bony thoracic wall and gives attachment to the
costal cartilages of the sternal (true) ribs as well as forming a place of origin for the
pectoral muscles. The sternum consists of segments called sternebrae which tend to fuse
together as age advances. The number of sternebrae varies with species as follows:
Pig: 6; Sheep: 6; Cow: 7; Goat: 7; Horse: 8
Sometimes the last one or two pair of ribs have no connection with other ribs at the
ventral end. Such ribs are called floating ribs. The spaces between the ribs are called
intercostal spaces. Figure below shows the Axial skeleton of cattle
Cervical
Thoracic
Sacrum
Lumbar
Skull
Coccygeal
Ribs
2.2. Appendicular skeleton: is made up of the bones of the limbs. Table below compares
the bones of the front (pectoral) limb to that of the hind (pelvic) limb by region.
Table: Comparison of Pectoral and Pelvic bones (Source: Spurgeon, 1992).
Pectoral limb
Pectoral girdle (shoulder girdle)
Scapula
Clavicle
Coracoid
Humerus-arm
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Pelvic limb
Pelvic girdle (os coxae)-pelvis
Ilium
Ishium
Pubis
Femur- thigh
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Radius-forearm
Ulna- forearm
CarpusMetacarpus- cannon
Phalanges- digits
Patella
Tibia- leg
FibulaTarsus- hock
Metatarsus- cannon
Phalanges- digits
Pectoral limbs:
• Scapula (shoulder blade)- in all animals, it is rather flat, triangular bone.
• Humerus (arm bone)- is a typical long bone that varies only in minor details
from one animal to another.
• Radius- is the larger of the two forearm bones, and the ulna is the smaller
mammal but not in birds. The radius is well developed in all species.
• Ulna- varies in its degree of development from species to species. In horse the
proximal portion of the shaft of the ulna is well developed but fused to the
radius. The cow, sheep, goat and pig each have a complete ulna, but with
restricted or no movement between the ulna and radius. The cat and dog have
considerably more movement between these complete bones, but not nearly as
much as man.
• Carpus- in all animals is a complete region that includes two rows of small
bones. Those in the proximal row are called radial, intermediate and ulnar.
Those in the distal row are numbered as 1,2,3, and 4. Bones fore limb and hind
limb are shown below.
Scapula
Pelvis
Humerus
Femur
Ulna
Tibia &
Radius
Fibula
Carpus
Tarsus
Metacarpus
Metatarsus
Digits
Bones of fore limb
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Digits
Bones of hind limb
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Skeleton of cattle
Anatomy of chicken
The domestic chicken is descendent of red jungle fowl. All systems are present but there
is modification of each system to meet the requirements of species. Modifications are
described below:
General modification
Cattle
1. Mouth
2. Fore limb
3. Long bones with marrow
4. Lungs and kidneys not attached
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Chicken
Beak
wings
without marrow, pneumatic
attached to dorsal wall
Presence of comb and wattle in head
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Beak
Comb
Wattle
Wing
Leg
Modification in chicken
Skeletal system
Is made up of bones that are pneumatic in nature making the body light for flight. Figure
below shows bones making skeletal system of chicken
Radius & ulna
Skull
Cervical vertebrae
Humerus
Pelvic bone
Femur
Sternum
Tibia
Metatarsus
Skeleton of chicken
Skeleton of pig
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Skeleton of goat
Skeleton of horse
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