Download DipaCH6 - THE SKELETAL SYSTEM

THE SKELETAL
SYSTEM
CH 6 – THE APPENDICULAR
SKELETON
FORELIMBS
 The
number of bones and their
development differs among species
 EXAMPLE:


Many species have DIGITS that are similar to
our fingers
Some species have HOOVES that encase
their digit or digits
• These animals are called UNGULATES
CLAVICLE
 COLLARBONE




Articulates medially with the sternum and
laterally with the scapula
Only well developed in animals that can
grasp (cats and primates)
Usually a vestigial remnant (relating to a
body part that has become small and lost its
use because of evolutionary change)
Both are fused in birds to form wishbone

SCAPULA (shoulder blade)


HUMERUS


Large triangular bone on the side of
the thorax
Long bone that extends from the
shoulder (articulates with scapula)
to the elbow (articulates with ulna
and radius)
ULNA




Located caudal to radius
Forms the elbow
Articulates with the humerus at the
OLECRANON (point of the elbow)
Fused to the radius in the HORSE

RADIUS
 Cranial to ulna
 Articulates with the humerus,
ulna, and carpal bones
 main load-bearing bone of
the lower forelimb

CARPUS
 Numerous short/irregular
bones arranged in 2 rows
 Refers to the entire wrist
including the joint
 Also called the KNEE in
large animals

METACARPALS
 Vary in number between species (Ex: dog – 5, horse – 3)
 Numbered from medial to lateral
rd metacarpal) that
 Horse has a CANNON BONE (3
articulates with the digit
 Small metacarpals are called SPLINT BONES in the horse
(smaller than the cannon and do not articulate with the
digit)- metacarpals 2 and 4

DIGITS





Numbered from medial to
lateral
PHALANGES are located
within the digits
Usually 3 phalanges in one
digit (P1, P2, P3)
Digit 1 (dewclaw) is often
removed in dogs
Horses have only one digit
(III) with 3 phalanx bones.
•
•
P1 and P2 are PASTERNS
P3 is the COFFIN BONE
 CLOVEN
hoofed animals have a split
hoof

2
Cow, pig, goats
metacarpals ( III and IV) which are fused
in the cow, and 2 complete digits (III and
IV) with 3 phalanx bones in each
 The other digits are vestigial
SESAMOIDS

Small bones
found with a joint
capsule or tendon

HORSE: Caudal
aspect of fetlock
(called proximal
sesamoids) and
caudal to P3
(navicular bone)

Patella is the
largest sesamoid
HINDLIMB
 Variations
exist between species in the
number and development of the bone
PELVIS

3 pairs of bones that fuse to
become one

IIium – the largest bone
• Flares out to the side



Ischium – strongest, most
caudal
Pubis – Most ventral
Connects to the sacrum at
the sacroiliac joint
 Pubic Symphysis is where
the paired pubic bones meet
 Acetabulum of the pelvis
forms the ball and socket joint
PELVIS
•Longest bone in the body
•Thigh
FEMUR

Articulates with the acetabulum
proximally to form the hip joint

Articulates with the tibia and patella
at the distal end of to form the
STIFLE JOINT (knee in humans)
 Kneecap
 Flat
sesamoid bone that glides over the
stifle joint in the patellar ligament at the
trochlea of the femur
PATELLA
TIBIA

Part of the shin

Located on medial aspect
of the leg

Articulates with the
femur proximally and the
tarsus and/or the fibula
distally, depending on the
species

Larger than fibula, more
weight bearing

Also part of the shin

Smaller than tibia

Small in size in the horse
and cow (doesn’t
articulate with tarsus in
these species)

Long and slender in shape

Articulates with the
femur proximally and the
tibia and/or tarsus
distally
FIBULA
TARSUS
 Ankle
 Called
HOCK in
animals
 Composed
of
numerous
irregularly shaped
bones arranged in
rows
METATARSALS
 Very
similar to
forelimb
 Vary in number
between species
 Numbered medial
to lateral
 Digits are also
very similar to
forelimb
JOINTS
– an articulation between bones
and cartilage that is held in place by
ligaments
 JOINT
A
joint may or may not have movement
 Classified
according to the degree of
movement that they allow and their tissue
structure
JOINTS

SYNARTHROSES (Fibrous joints)
• no movement
• Ex: Skull

AMPHIARTHROSES (Cartilaginous
joints)
• slight movement
• Ex: Pelvis at pubic symphysis, vertebral column

DIARTHROSES (Synovial joints)
• freely movable, but not all in the same manner
• Most numerous in the body
• Ex: Hip joint, shoulder joint
JOINTS – terms on page 92