THE SKELETAL SYSTEM
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Framework of the body
Joints connect the bones
Osteology
Functions
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Protection of the vital organs
Base for general structure and outline
Body rigidity
Some acts as a lever
Storage site for minerals
Bones contain marrow that plays a part in the formation of
blood cells
Bone Anatomy
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Diaphysis – the body of a long bone
Epiphysis – enlarged ends of long bones
Metaphysis – joining point of diaphysis and epiphysis
Periosteum – the thin outer protective layer of bone
Medullary Cavity – space within bone filled with marrow
Endosteum – thin inner protective layer lining the medullary
cavity
7. Marrow – red and yellow; red bone marrow contains blood
stem cells that can become red blood cells, white blood cells, or
platelets
Composition of Bone
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Adult bone is 25% water, 45% mineral, and 30% organic
matter
Calcium constitutes about 37% of the mineral content of bone
Phosphorus accounts 18% of the mineral content of bone
Organic fraction of bone is about 90% collagen which is
converted to gelatin when heated in an aqueous solution
General parts
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Axial skeleton and appendicular skeleton
Axial skeleton includes skull, vertebra and ribs
Appendicular skeletons are made up of bones of the limbs
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Axial – central axis bones
1. Maxilla
2. Mandible
3. Ribs
4. Cervical
5. Thoracic
Pectoral – bones of the forelimbs
1. Scapula
2. Humerus
3. Radius
Pelvic – bones of the hind limbs
1. Ilium
2. Pelvis
3. Ischium
4. Femur
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4. Carpus
5. Ulna
6. Metacarpus
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Axial Skeleton
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Lumbar
Sternum
Caudal
Sacrum
Skull
- Many plates of bones fused together
- Fontanel – soft spot-on top of the skull
Tarsus
Tibia
Metatarsus
Patella
2. Vertebrae
- Have five regions:
a. Cervical – vertebrae of the neck region
➢ Atlas (C1) – first cervical vertebra; forms the
joints that let you nod ‘yes’
➢ Axis (C2( – second cervical vertebra; forms the
joints that let you nod ‘no’
~ there are seven cervical vertebrae in all mammals
b. Thoracic – vertebrae of the body; always have a rib
attached and a spine on top
➢ ‘true ribs’ – directly attach to sternum with
cartilage
➢ ‘false ribs’ – connect to each other with
cartilage, not the sternum
➢ ‘ floating ribs’ – seen in the dog; have cartilage
on the tips but do not attach to anything
c. Lumbar – vertebrae of the lower back; carnivores
generally tend to have more to lend greater flexibility;
herbivores need to have a short, strong back to
support large digestive and reproductive organs
d. Sacral – vertebrae of the pelvic; fused together on
the ventral side; herbivores generally tend to have
more to add strength and support to the back;
carnivores tend to have less for flexibility
e. Coccygeal – vertebrae of the tail region; used for
balance; become smaller at the end of the tail
Appendicular Skeleton
1. Forelimb
a. Scapula – ‘shoulder blade’ attached to muscle
b. Clavicle – cat is the only domestic animal
c. Avian –
d. Humerus – forms the upper arm
e. Radius – forms the forearm
f. Ulna – forms the elbow joint
g. Carpus – ‘knee’ in the horses; ‘wrist’ in dogs and humans
2. Metacarpals – cannon region of the forelimb; long, thin bones
that are located between the carpal bones in the wrist and the
phalanges in the digits
3. Phalanx
a. Proximal phalanx (P1) – bones of the finger, hoof, claw
b. Intermediate phlanx (P2)
c. Distal phalanx (P3) – coffin bone in horses
4. Sesamoids – bones embedded in tendons
a. Proximal sesamoids – tucked behind P1
b. Distal sesamoid – tucked in underneath P3
5. Hind Limb
a. Pelvis
➢ Tuber coxae – forms the ‘point of hip’
➢ Ischiatic tuberosity – forms the ‘seat bones’
b. Femur
c. Patella – forms the ‘stifle’ joint in horses; ‘knee’ in dogs
d. Tibia – large bone of the lower leg, extending from the
knee to the ankle
e. Fibula – fused with the tibia and considered vestigial in
herbivores
f. Tarsus – ‘hock’; equivalent to the human ‘ankle’
g. Metatarsal – cannon region in the hind limb
Classifications of Bones
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Long bones
- i.e. Femur, tibia, humerus
- composed of compact bone and spongy bone
- compact bone appears to be solid while spongy bone has
the appearance of a sponge
Short bone
- i.e. carpus and tarsus
- Cube-shaped
Flat bone
- Plate of bone
- i.e. scapula, rib, skull
Irregular bone
- i.e. vertebrae
- complex-shaped
sesamoid
- i.e. proximal and distal sesamoids, patella
- small, seed-shaped bone
Joints and Synovial Fluid
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Connection between any of the skeletons rigid component parts
is known as joint, also described as an articulation
~ study of joints is termed arthrology and inflammation of
joints is termed arthritis – common malady among domestic
animals
Synovial joints are those that allow surfaces to slide past one
another.
~ facilitated by the presence of articular cartilage on each
bone surface of the articulation and by presence of synovial
fluid
~ enclosed by a joint capsule
~ is contained within joint capsule and is secreted by its inner
membrane, the synovial membrane
~ outer layer of the joint capsule is a fibrous layer that extends
from the periosteum of each bone and contributes to the
stability of the joint. A meniscus within the joint capsule serves
a cushioning function.