1. CH 6 – THE APPENDICULAR SKELETON
THE SKELETAL SYSTEM
CH 6 – THE APPENDICULAR SKELETON

2. 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

3. 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

4. SCAPULA (shoulder blade)
Large triangular bone on the side of the thorax
HUMERUS
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

5. 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

6. METACARPALS
Vary in number between species (Ex: dog – 5, horse – 3)
Numbered from medial to lateral
Horse has a CANNON BONE (3rd metacarpal) that 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

7. 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

8. CLOVEN hoofed animals have a split hoof
Cow, pig, goats
2 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

9. 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

10. HINDLIMB
Variations exist between species in the number and development of the bone

11. 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

12. PELVIS

13. FEMUR Longest bone in the body Thigh
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)

14. Kneecap
Flat sesamoid bone that glides over the stifle joint in the patellar ligament at the trochlea of the femur
PATELLA

15. 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

16. FIBULA 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

17. TARSUS Ankle Called HOCK in animals
Composed of numerous irregularly shaped bones arranged in rows

18. METATARSALS Very similar to forelimb Vary in number between species
Numbered medial to lateral
Digits are also very similar to forelimb

19. JOINTS
JOINT – an articulation between bones and cartilage that is held in place by ligaments
A joint may or may not have movement
Classified according to the degree of movement that they allow and their tissue structure

20. 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

21. JOINTS – terms on page 92