Skeletal System:
The skeleton is a framework of structures, made of
bones and cartilage that support and protect the body.
Axial Skeleton: includes the skull, vertebrae, ribs, and
sternum.
• Skull – many plates of bone fused together. The
soft spot on top of the skull is called a
fontanel.
• Vertebrae – have five distinct regions:
1. Cervical – vertebrae of the neck region
Atlas – called “C1”, the first cervical
vertebra. Forms the joint that lets
you nod “yes”.
Axis – called “C2”, the second cervical
vertebra. Forms the joint that lets
you nod “no”.
There are seven cervical vertebrae in all
mammals – even the giraffe!
2. Thoracic – vertebrae of the body region,
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.
3. Lumbar – vertebrae of the lower back
Carnivores generally tend to have more –
perhaps to lend greater flexibility.
Herbivores need to have a short, strong back
to support large digestive and reproductive
organs.
4. Sacral – vertebrae of the pelvic region
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.
5. Coccygeal – vertebrae of the tail region
Used for balance.
Become smaller at the end of the tail.
Appendicular Skeleton – the fore and hind limbs
• Forelimb
1. Scapula – “shoulder blade” attached with
muscle
2. Clavicle – the cat is the only domestic animal
with a clavicle!
3. Humerus – forms the upper arm
4. Ulna – forms the elbow joint, fused with the
radius in herbivoires
6. Carpus – commonly called the “knee” in
horses, the “wrist” in dogs and
humans
7. Metacarpals – commonly called the cannon
region of the forelimb.
Number depends on species:
a) Humans: 5
b) Horses: 1 plus 2 accessory
metacarpals, called “splint bones”
c) Dogs and cats: 4 plus the dewclaw
d) Cattle: 1 that splits at bottom into a
cloven hoof and two dewclaws
e) Pigs: 4 (2 toes and 2 dewclaws)
8. Proximal phalanx (P1) – bones of the finger,
hoof, and claw
9. Intermediate phalanx (P2)
10. Distal phalanx (P3) – the coffin bone in
horses
11. Proximal sesamoids – tucked in behind P1
12. Distal sesamoid – tucked in underneath P3,
(called the navicular bone in horses)
• Hind limb
13. Pelvis
a) Tuber coxae – part of pelvis that
forms the “point of hip”
b) Ischiatic tuberosity- part of pelvis
that forms the “seat bones”
14. Femur
15. Patella – forms the “stifle” joint in horses,
sometimes called the “knee” in
dogs, equivalent to the human knee
16. Tibia – main bone of the gaskin of the horse
17. Fibula – fused with the tibia & considered
vestigial in herbivores
18. Tarsus – commonly called the “hock”,
equivalent to the human “ankle”
19. Metatarsal – cannon region in the hind limb.
Number depends on species.
20. P1
21. P2
22. P3
23. Proximal and distal sesamoids
Classification of Bones:
• Short bone – cube shaped, i.e. carpus and tarsus
• Flat bone – plate of bone, i.e. scapula, rib, skull
• Irregular bone – complex shaped, i.e. vertebrae
• Sesamoid – small, seed-shaped bone, i.e. proximal
and distal sesamoids, patella
• Long bone – bone is longer that it is wide, i.e.
femur, tibia, humerus, etc.
Bone Anatomy:
• Diaphysis – body of a long bone
• Epiphysis – enlarged ends of long bones
• Metaphysis – joining point of diaphysis and
epiphysis
• Periosteum – thin outer protective layer of bone
• Medullary cavity – space within bone filled with
marrow
• Endosteum – thin inner protective layer lining the
medullary cavity
Bone Growth:
• Occurs in the epiphysis of long bones.
• Epiphyseal growth plates produce cartilage, which
gradually turns into bone via a process called
ossification.
Fractures:
Major categories
• Simple – bone does not break skin.
• Compound – bone breaks through skin, much
more serious.
• Complete – fracture goes completely across the
bone.
• Incomplete – fracture does not go completely
across bone.
Classifying fractures
• Fissure fracture: incomplete break, along the long
axis of the bone
• Greenstick fracture: incomplete break on one side
of a bone, usually due to a
bending force
• Transverse fracture: break across the bone
• Comminuted fracture: bone shatters into many
pieces
Healing fractures
Bone cells lay down a material called fibrocartilage,
which gradually turns into bone in a process called calcification.