CH 6 – THE APPENDICULAR SKELETON 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) 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

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 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

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 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

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

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)

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

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

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 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

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