Compare the attachment of fore and hind limbs to the body and give reasons for the differences.
-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.)
Differentiate between extrinsic and intrinsic muscles and give examples of each.
- 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
What is the main weight bearing forelimb extrinsic muscle?
Serratus ventralis
How does the horse reduce gravitational stress on the serratus ventralis m.?
-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)
Discuss the three common nerve damage syndromes of the upper forelimb:
-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
What is the structure and function of the lacertus fibrosus.
- 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
Compare hind and forelimb stay apparatus structure and function.
- 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.
Compare radius and ulna fusion in various domestic species.
- 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
How is bone maturity for racing determined in the horse?
Radiology of distal radial physis used
What is the significance of absence of the clavicle in quadrapeds?
-Allows the shoulder to not be fixed, allowing for a much more mobile scapula to increase stride length (and therefore speed)
What muscles cause advancement and retraction of the entire forelimb?
- Advancement: caused by brachiocephalicus
- Retraction: caused by deep pectoral m. (ascending) and latissimus mm.
What are the principle inputs and outputs of the brachial plexus
- Inputs: numbered nerves- C5,6,7,8; T1,2
- Outputs: named nerves-suprascapular, thoracodorsal, subscapular, axillary, median, ulnar, radial, musculocutaneous
Differentiate between the flexor and extensor epicondyles of the humerus
- Flexor: medial epicondyle; origin of antebrachial flexor mm.
- Extensor: lateral epicondyle; origin of antebrachial extensor mm.
What is the chestnut?
Thickening of skin with no hair on it
Compare fore and hind limb chestnuts. What are they homologous to?
- 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
