THE SKELETAL SYSTEM

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THE SKELETAL SYSTEM

• CH 6 THE APPENDICULAR SKELETON

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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

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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

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• 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

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• 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

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• 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

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• 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

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• 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

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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

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HINDLIMB

• Variations exist between species in the number
  and development of the bone

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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

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PELVIS
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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)

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PATELLA

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

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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

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FIBULA

• Also part of the shin
• Smaller than tibia
• Small in size in the horse and cow (doesnt
  articulate with tarsus in these species)
• Long and slender in shape
• Articulates with the femur proximally and the
  tibia and/or tarsus distally

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TARSUS

• Ankle
• Called HOCK in animals
• Composed of numerous irregularly shaped bones
  arranged in rows

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METATARSALS

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

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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

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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

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JOINTS terms on page 92