Chapter 7

Question 1

Compare the attachment of fore and hind limbs to the body and give reasons for the differences.

Answer 1

-strong attachment of the hind quarters to the vertebrae via the sacro-iliac joint, but there is no bony attachment of the forelimb to axial skeleton; this allows for a mobile scapula( incr. stride length and shock absorption (due to musc. attach.)

Question 2

Differentiate between extrinsic and intrinsic muscles and give examples of each.

Answer 2

• Extrinsic muscles attach the limb to the body: serratus ventralis, deep pectoral, latissimus dorsi, brachiocephalicus
• Intrinsic muscles make attachments only w/in the limb; brachialis, biceps brachii, shoulder muscles, extensor carpi radialis

Question 3

What is the main weight bearing forelimb extrinsic muscle?

Answer 3

Serratus ventralis

Question 4

How does the horse reduce gravitational stress on the serratus ventralis m.?

Answer 4

-reduced through the forelimb stay apparatus (connections of central tendon of biceps through the lacertus fibrosus to the extensor carpi radialis; this fixes the shoulder and carpal joints)

Question 5

Discuss the three common nerve damage syndromes of the upper forelimb:

Answer 5

-Sweeny: damage to suprascapular n.; assoc. w/ a horse collar; supplies infraspinatous and supraspinatus mm.
-Radial n. paralysis: supplies all intrinsic extensors; distal part vulnerable to damage where wraps around humerus caud. to brachialis m.
Brachial plexus paralysis: occurs when animal is in lateral recumbency w/ the downside shoulder against the ribcage

Question 6

What is the structure and function of the lacertus fibrosus.

Answer 6

• long tendon of biceps; connects central tendon of biceps to extensor carpi radialis
• continuous tendon extending from metacarpus to scapula; fixes the shoulder and carpal joints w/ little or no effect on elbow joint
• basis of forelimb stay appart

Question 7

Compare hind and forelimb stay apparatus structure and function.

Answer 7

• Hind: stifle/patella lock mechanism, SDF and suspensory apparatus; locks one leg at a time
• Fore: biceps tendon, lacertus fibrosus, extensor carpi radialis, and suspensory apparatus; both legs are fixed at same time so support tripod establ.

Question 8

Compare radius and ulna fusion in various domestic species.

Answer 8

• Pig: fibrous fusion of radius and ulna
• Cow: bony fusion of radius and ulna
• Horse: bony fusion; distal part of ulna is absorbed w/in radius
• Primates: radius rotates around ulna
• Carnivores: limited rotation

Question 9

How is bone maturity for racing determined in the horse?

Answer 9

Radiology of distal radial physis used

Question 10

What is the significance of absence of the clavicle in quadrapeds?

Answer 10

-Allows the shoulder to not be fixed, allowing for a much more mobile scapula to increase stride length (and therefore speed)

Question 11

What muscles cause advancement and retraction of the entire forelimb?

Answer 11

• Advancement: caused by brachiocephalicus

- Retraction: caused by deep pectoral m. (ascending) and latissimus mm.

Question 12

What are the principle inputs and outputs of the brachial plexus

Answer 12

• Inputs: numbered nerves- C5,6,7,8; T1,2

- Outputs: named nerves-suprascapular, thoracodorsal, subscapular, axillary, median, ulnar, radial, musculocutaneous

Question 13

Differentiate between the flexor and extensor epicondyles of the humerus

Answer 13

• Flexor: medial epicondyle; origin of antebrachial flexor mm.
• Extensor: lateral epicondyle; origin of antebrachial extensor mm.

Question 14

What is the chestnut?

Answer 14

Thickening of skin with no hair on it

Question 15

Compare fore and hind limb chestnuts. What are they homologous to?

Answer 15

• Located higher in the forelimb (above carpus, on medial side of antebrachium about middle of its length) than the hind limb (below the hock, on medial side of distal tarsus)
• Likely a remnant of carpal/tarsal pad