Thoracic Limb (Large Animal)

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Questions and Answers

What percentage of a horse's body weight is placed on its thoracic limbs?

60% (correct)

50%

70%

40%

What is the common name of the metacarpal 3 bone in horses?

Cannon bone (correct)

Navicular bone

Greater Tubercle

Splint bone

Which of the following bones is no longer discernable at the distal radius in horses?

Scapula

Humerus

Ulna (correct)

Radius

What is the term for the fibrous mechanism that allows horses to oppose gravity without expending energy?

Stay apparatus Signup and view all the answers

Which type of walker bears weight on their digits, metatarsals, and plantar tarsus?

Plantigrade walker Signup and view all the answers

What is the approximate location of a horse's center of gravity?

15th thoracic vertebrae Signup and view all the answers

What is the common name of the metacarpal 2 and 5 bones in horses?

Splint bones Signup and view all the answers

What is the name of the bone referred to as the 'Navicular' bone in horses?

Distal sesamoid bone Signup and view all the answers

In dogs, which carpal bones are fused?

Radial and intermediate carpal bone Signup and view all the answers

In ox (cows), which metacarpal bones bear weight?

Metacarpal 3 and 4 Signup and view all the answers

What is the common name of the carpus in horses?

Knee Signup and view all the answers

Which muscle elongation is required for flexion of the carpus?

Deep digital flexor muscle Signup and view all the answers

What is another name for the elbow joint?

Humeroradioulnar joint Signup and view all the answers

What is the common name of the Proximal Interphalangeal joint?

Pastern joint Signup and view all the answers

What is the primary function of the stay apparatus?

To reduce the energy required to stand Signup and view all the answers

What is the primary function of the proximal and distal check ligaments?

To counteract hyperextension of the fetlock joint Signup and view all the answers

Where does the suspensory ligament originate?

Proximal metacarpus Signup and view all the answers

What is the shape of the straight sesamoidean ligament?

I shape Signup and view all the answers

What is the function of the suspensory apparatus?

To stabilize the fetlock, pastern, and coffin joints Signup and view all the answers

Which of the following is NOT a part of the suspensory apparatus?

Lacertus fibrosis Signup and view all the answers

What is the function of the distal sesamoidean ligaments?

To counteract hyperextension of the fetlock joint Signup and view all the answers

What is the primary function of the stay apparatus in the elbow joint?

To prevent elbow flexion while under weight Signup and view all the answers

What covers the proximal sesamoid bones?

Scutum Signup and view all the answers

What is the role of the triceps muscle during standing rest?

To remain relatively flaccid Signup and view all the answers

What is the shape of the cruciate sesamoidean ligament?

X shape Signup and view all the answers

What is the purpose of the lacertus fibrosus?

To transmit tension from the biceps brachii muscle to the extensor carpi radialis muscle Signup and view all the answers

What is the primary function of the palmar carpal ligament?

To prevent carpal hyperextension Signup and view all the answers

What is the consequence of the shoulder being 'locked'?

The forces of the humerus rest on a nearly vertical radius Signup and view all the answers

What is the result of the body weight balancing on the radius in a 'crooked post'?

Minimal force acts on the elbow to flex or extend Signup and view all the answers

What is the attachment point of the palmar carpal ligament?

From the distal radius to the proximal metacarpal 3 bone Signup and view all the answers

Match the number to the correct term, in regards to the distal equine limb.

1 = Flexed carpal joint 2 = Extended carpal joint 3 = Flexed fetlock joint 4 = Extended fetlock joint Signup and view all the answers

What is number 1 referring to?

Proximal check ligament Signup and view all the answers

What is number 2 referring to?

Distal check ligament Signup and view all the answers

Match the number to the correct term, in regards to the Stay Apparatus

2 = DDF tendon 4 = Suspensory ligament 1 = SDF tendon 3 = Distal check ligament Signup and view all the answers

What is number 5 referring to?

Lateral digital extensor ligament Signup and view all the answers

Match the number to the correct term, in regards to the distal sesamoidean ligaments.

1 = Straight 2 = Cruciate 3 = Oblique Free match = Free match Signup and view all the answers

Which species has bone number 1?

Equine Signup and view all the answers

Which species has bone number 2?

Bovine Signup and view all the answers

Study Notes

Large Animal: General Info

Large animals, such as horses, experience a downward force due to their body weight.
The "stay apparatus" is a fibrous mechanism that allows them to oppose gravity without expending energy.
Approximately 60% of the horse's body weight is placed on the thoracic limbs.

Walking Postures

Digitigrade walkers bear weight on their digits (e.g., dogs and cats).
Unguligrade walkers bear weight on the distal phalanx (e.g., horses and cattle).
Plantigrade walkers bear weight on their digits, metatarsals, and plantar tarsus (e.g., humans, bears, squirrels, and skunks).

Bones: Thoracic Limb

Bones of the large animal thoracic limb include the scapula, humerus, radius, ulna, carpus, metacarpus, phalanges, and proximal and distal sesamoid bones.
In horses, the distal sesamoid bone is referred to as the "Navicular" bone.
The radius and ulna are almost completely fused, and the ulna is no longer discernible at the distal radius.
The point of the shoulder can be referenced by the Greater Tubercle of the humerus.
Their approximate center of gravity is located at the 15th thoracic vertebrae.
The metacarpal 3 bone has the common name of the "Cannon" bone, which they primarily weight bear on.
The metacarpal 2 and 5 bones have the common name of the "Splint" bones.

Joints: Horse Thoracic Limb

The Shoulder joint is referred to as the "Glenohumeral" joint.
The Elbow (or cubital) joint is referred to as the "Humeroradioulnar" joint.
The Proximal Interphalangeal joint has the common name of the "Pastern" joint.
The Distal Interphalangeal joint has the common name of the "Coffin" joint.
The Metacarpophalangeal joint has the common name of the "Fetlock" joint.
The Carpal (or antebrachiocarpal) joint is composed of the middle carpal joint and the metacarpophalangeal joint.

Stay Apparatus: General Info

The stay apparatus reduces the energy required to stand, allowing rest while standing.
It makes movement efficient via specific groups of muscles and tendons/ligaments working in synchrony to conserve energy.
The stay apparatus allows horses to doze while standing up, using minimal muscular energy.
The coordination of many individual structures acts to "lock" the limb in extension, preventing collapse despite minimal effort.

Stay Apparatus: Shoulder Joint Stabilization

The shoulder joint is stabilized by preventing flexion.
The tendon of the biceps brachii muscle prevents the shoulder from flexing.

Stay Apparatus: Elbow Joint Stabilization

Elbow joint stabilization involves preventing elbow flexion while under weight.
The shoulder being "locked" allows the body weight to balance on the radius in a "crooked post".

Stay Apparatus: Carpal Joint Stabilization

Carpus stabilization involves preventing the carpus from flexing or extending.
Tension on the biceps brachii muscle is transmitted to the extensor carpi radialis muscle via the "lacertus fibrosus".
The strong palmar carpal ligament aids in preventing hyperextension of the carpal joint.

Stay Apparatus: Check Ligaments

Tension on the SDF (superficial digital flexor) and DDF (deep digital flexor) tendons are "checked" by the accessory ligaments, which are attached to these tendons.

Stay Apparatus: Fetlock, Pastern, and Coffin Joint Stabilization

The stabilization of the fetlock, pastern, and coffin joint is due to the suspensory apparatus, which involves the prevention of hyperextension of these joints.
The interosseus muscle (also known as the suspensory ligament) prevents hyperextension of the fetlock joint.

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Description

Learn about the unique anatomy of large animals, including the stay apparatus and its role in supporting their body weight, and how it distributes the weight between their limbs.